X CBSE Science Tutorials

Table of Contents

Table of Contents – Chemistry CHAPTER 01: CHEMICAL REACTIONS AND EQUATIONS .................................. 1 CHAPTER M AP: ........................................................................................................................................... 1 INTRODUCTION: ........................................................................................................................................... 1 Chemical Equations: ......................................................................................................................... 1 What is a word-equation? ............................................................................................................ 2 Writing a Chemical Equation: ....................................................................................................... 2 Types of Chemical Reactions:........................................................................................................... 4 Combination Reaction: ................................................................................................................. 4 Decomposition Reaction: ............................................................................................................. 4 Displacement Reaction: ............................................................................................................... 5 Double Displacement Reaction: ................................................................................................... 5 Oxidation and Reduction Reactions: ............................................................................................ 6 APPENDIX: NCERT ACTIVITIES ................................................................................................................... 7 REVIEW QUESTIONS: ................................................................................................................................. 10 NCERT EXERCISE: ................................................................................................................................... 11 MULTIPLE CHOICE QUESTIONS: PRACTICAL (THEORY) ............................................................................... 13 ANSWERS: ................................................................................................................................................ 14

CHAPTER 02: ACIDS, BASES AND SALTS.......................................................... 16 CHAPTER M AP: ......................................................................................................................................... 16 Properties of Acids and Bases: .................................................................................................. 16 Comparative properties of all Acids and Bases: ........................................................................ 17 Bleaching Powder: .......................................................................................................................... 21 Baking Soda (Sodium Bicarbonate): ............................................................................................... 21 Plaster of Paris: ............................................................................................................................... 23 APPENDIX: NCERT ACTIVITIES ................................................................................................................. 23 REVIEW QUESTIONS: ................................................................................................................................. 29 NCERT EXERCISE: ................................................................................................................................... 33 MULTIPLE CHOICE QUESTIONS: PRACTICAL THEORY .................................................................................. 34 ANSWERS: ................................................................................................................................................ 41

CHAPTER 03: METALS AND NON–METALS ....................................................... 43 CHAPTER M AP: ......................................................................................................................................... 43 INTRODUCTION: ......................................................................................................................................... 43 METALS: ................................................................................................................................................... 44 NON–METALS: .......................................................................................................................................... 44 Metalloids ........................................................................................................................................ 44 Comparative Properties – Metals and Non Metals:......................................................................... 44 Reactions of Metals: ........................................................................................................................ 45 Activity Series of Metals: ................................................................................................................. 47 METALLURGY: .......................................................................................................................................... 50 Conversion to Metal Oxide: ............................................................................................................. 52 Reduction: ....................................................................................................................................... 53 Universal Tutorials – X CBSE (2012–13) – Chemistry

Refining of Metals (Purification of Metals):...................................................................................... 55 Corrosion: ........................................................................................................................................ 55 Alloys: .............................................................................................................................................. 56 Steel: .......................................................................................................................................... 57 Alloying of Gold: ......................................................................................................................... 57 NON METALS: ........................................................................................................................................... 58 Importance:...................................................................................................................................... 58 Chemical Properties of Non Metals: ................................................................................................ 58 APPENDIX: NCERT ACTIVITIES ................................................................................................................. 58 REVIEW QUESTIONS: CLASS WORK ............................................................................................................ 61 REVIEW QUESTIONS: HOME WORK ............................................................................................................. 64 NCERT EXERCISE: ................................................................................................................................... 68 MULTIPLE CHOICE QUESTIONS: PRACTICAL THEORY.................................................................................. 69 ANSWERS: ................................................................................................................................................ 75

Universal Tutorials – X CBSE (2012–13) – Chemistry

Table of Contents

Table of Contents – Biology CHAPTER 06: LIFE PROCESSES ......................................................................... 77 CHAPTER M AP: ......................................................................................................................................... 77 LIFE PROCESSES: ..................................................................................................................................... 78 NUTRITION: ............................................................................................................................................... 79 Modes of Nutrition: .......................................................................................................................... 79 Nutrition in Animals: ........................................................................................................................ 82 Nutrition in Amoeba: ................................................................................................................... 82 Human digestive system: ........................................................................................................... 82 APPENDIX: ................................................................................................................................................ 85 RESPIRATION: ........................................................................................................................................... 87 Types of Respiration: ...................................................................................................................... 87 Respiration in Plants: ...................................................................................................................... 88 Respiration in Animals:.................................................................................................................... 88 Aquatic animals: ......................................................................................................................... 88 Terrestrial animals: ..................................................................................................................... 88 Human Respiratory System: ........................................................................................................... 89 Mechanism of Breathing: ........................................................................................................... 90 Exchange of Gases in Tissues:.................................................................................................. 90 APPENDIX: ................................................................................................................................................ 91 TRANSPORTATION: .................................................................................................................................... 92 Transportation in Humans: .............................................................................................................. 92 Structure and Function of Heart and Blood Vessels: ................................................................. 93 Blood Vessels:............................................................................................................................ 94 Lymphatic System: ..................................................................................................................... 95 Transportation in Plants: ................................................................................................................. 96 Raw Materials and Source: ........................................................................................................ 96 Transportation of Food and other Substances: .......................................................................... 97 APPENDIX: ................................................................................................................................................ 98 EXCRETION: .............................................................................................................................................. 99 Excretion in Humans: ................................................................................................................. 99 Excretion in Plants:........................................................................................................................ 101 NCERT EXERCISE: ................................................................................................................................. 101 PREVIOUS BOARD QUESTIONS: ............................................................................................................... 102 MISCELLANEOUS EXERCISES:.................................................................................................................. 105 MULTIPLE CHOICE QUESTIONS: PRACTICAL THEORY................................................................................ 108

CHAPTER 07: CONTROL AND CO-ORDINATION .............................................. 119 CHAPTER M AP: ....................................................................................................................................... 119 CO–ORDINATION IN PLANTS AND ANIMALS: .............................................................................................. 119 Coordination in Animals: ............................................................................................................... 119 Human Nervous System: .............................................................................................................. 120 Function of Human Nervous System: ...................................................................................... 120 Neuron - Functional Unit of the Nervous System:.................................................................... 120 Components of Nervous System: ................................................................................................. 122 Central Nervous System (CNS): .............................................................................................. 122 Reflex Action: ................................................................................................................................ 124 Hormones: ..................................................................................................................................... 124 Hormonal control by feedback Mechanism: .................................................................................. 125 Coordination in Plants: .................................................................................................................. 125 APPENDIX: .............................................................................................................................................. 126 Volume

Universal Tutorials – X CBSE (2012–13) – Biology

NCERT EXERCISE: ................................................................................................................................. 127 PREVIOUS BOARD QUESTIONS: ............................................................................................................... 128 MISCELLANEOUS EXERCISE: ................................................................................................................... 129


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Table of Contents – Physics CHAPTER 12: ELECTRICITY ............................................................................... 131 CHAPTER M AP: ....................................................................................................................................... 131 INTRODUCTION: ....................................................................................................................................... 131 CURRENT ELECTRICITY: .......................................................................................................................... 132 Classification of Substances: ........................................................................................................ 132 Electric Potential and Potential Difference: ................................................................................... 132 ELECTRIC CIRCUITS: ............................................................................................................................... 133 OHM’S LAW: ........................................................................................................................................... 134 Verification of Ohm’s Law: ....................................................................................................... 134 RESISTANCE: .......................................................................................................................................... 134 Concept of Resistance: ................................................................................................................. 135 Methods of joining Resistors: ........................................................................................................ 136 Resistors in Series: .................................................................................................................. 136 Resistors in Parallel: ................................................................................................................ 136 HEATING EFFECT OF ELECTRIC CURRENT: ............................................................................................... 137 Joule’s law for heating effect of electric current: ........................................................................... 137 Applications of heating effect of current: ....................................................................................... 138 Electric bulb: ............................................................................................................................. 138 Electric Fuse:............................................................................................................................ 138 Electric Power: .............................................................................................................................. 138 Useful Conversions: ................................................................................................................. 139 APPENDIX: .............................................................................................................................................. 139 SOLVED EXAMPLES:................................................................................................................................ 142 REVIEW QUESTIONS: ............................................................................................................................... 146 NCERT QUESTIONS: .............................................................................................................................. 151 PREVIOUS BOARD QUESTIONS: ............................................................................................................... 153 ANSWERS TO UNSOLVED EXERCISES:...................................................................................................... 156

CHAPTER 13: MAGNETIC EFFECTS OF CURRENT.......................................... 158 CHAPTER M AP: ....................................................................................................................................... 158 INTRODUCTION: ....................................................................................................................................... 158 M AGNETIC EFFECTS OF ELECTRIC CURRENT: .......................................................................................... 159 Oersted’s Experiment: ................................................................................................................... 159 Magnetic field due to a straight wire carrying electric current: ...................................................... 159 Factors affecting the magnetic field produced due to current: ................................................. 160 Magnetic field due to a Solenoid: .................................................................................................. 160 EFFECTS OF EXTERNAL FIELD ON A WIRE CARRYING CURRENT: ................................................................ 161 Fleming’s Left hand Rule:.............................................................................................................. 161 Factors to increase the force: ........................................................................................................ 162 ELECTRIC MOTOR: .................................................................................................................................. 162 ELECTROMAGNETIC INDUCTION: .............................................................................................................. 163 Fleming’s Right Hand Rule:........................................................................................................... 163 Factors to increase the strength of induced current:................................................................ 163 Domestic Electric Circuits:............................................................................................................. 165 APPENDIX: .............................................................................................................................................. 165 SOLVED EXAMPLES:................................................................................................................................ 168 REVIEW QUESTION: ................................................................................................................................. 169 NCERT QUSESTIONS: ............................................................................................................................ 173 PREVIOUS BOARD QUESTIONS: ............................................................................................................... 174 ANSWERS TO UNSOLVED EXERCISES:...................................................................................................... 176 Volume

Universal Tutorials – X CBSE (2012–13) – Physics

CHAPTER 14: SOURCES OF ENERGY............................................................... 177 CHAPTER M AP: ....................................................................................................................................... 177 INTRODUCTION: ....................................................................................................................................... 177 A good source of energy: .............................................................................................................. 178 Conventional Sources of Energy:............................................................................................. 178 Fossil Fuels: .................................................................................................................................. 178 Disadvantages:......................................................................................................................... 178 Pollution Control: ...................................................................................................................... 179 Traditional sources of energy: ....................................................................................................... 179 Thermal Power Plant: ............................................................................................................... 179 Hydro Power Plants: ................................................................................................................ 179 Improvements in Technology for using Conventional Sources of Energy: ................................... 180 Bio-Mass: ................................................................................................................................. 180 Wind Energy: ............................................................................................................................ 181 Non–conventional Sources: .......................................................................................................... 181 Solar Energy:............................................................................................................................ 182 Energy from Sea: .......................................................................................................................... 184 Forms of energy from Sea: ...................................................................................................... 184 Geothermal Energy: ...................................................................................................................... 185 Nuclear Energy: ............................................................................................................................. 185 Environmental Consequences: ..................................................................................................... 185 How long will an energy source last us? ....................................................................................... 186 REVIEW QUESTION: ................................................................................................................................. 186 NCERT QUESTIONS: .............................................................................................................................. 188 PREVIOUS YEARS’ BOARD QUESTIONS ..................................................................................................... 189 APPENDIX: .............................................................................................................................................. 190 ANSWERS TO THE UNSOLVED EXERCISE: ................................................................................................. 192

PRACTICAL SKILLS IN SCIENCE AND TECHNOLOGY .................................... 193 ELECTRICITY AND M AGNETISM: ............................................................................................................... 193


Volume

Chapter 01: Chemical Reactions and Equations

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Chapter 01: Chemical Reactions and Equations Chapter Map: → Chemical Equations → Writing a Chemical Equation → Balancing Chemical Equations → Types of Chemical Reactions → Combination Reactions → Decomposition Reactions → Displacement Reactions → Double Displacement Reactions → Oxidation and Reduction Reactions → The effects of Oxidation Reactions in Everyday Life → Corrosion → Rancidity

Introduction:  Chemical reactions are taking place very frequently in our day to day life. E.g. mangoes changing their colour from green to yellow (broadly ripening of all fruit), milk left at room temperature during summer (it curdles) an iron nail or tawa/ pan exposed to humid air (rusts, oxidizes) grapes fermenting, food being cooked and digested, respiration of living organisms etc.  In all the above examples the characteristics of all the substances taking part in the reaction (physical and chemical) have changed along with their identity. When their physical form changes we say that a physical reaction has taken place. However when their chemical nature/ properties changes and a new substance/s are formed we say that a chemical reaction has taken place.  When a magnesium ribbon is burnt in oxygen, it gets converted to magnesium oxide. This is a word statement. However, it can be written as a chemical equation as 2Mg + O2 → 2MgO.

Chemical Equations:  Observations to determine whether a chemical reaction has taken place. When a chemical reaction takes place we observe the following:  Change in state of reactants  Change in colour of reactants  Evolution of a gas as a product  Change in temperature of the entire reaction.  The word-equation for the reaction when Magnesium reacts with oxygen to give us Magnesium oxide would be Magnesium + Oxygen → Magnesium oxide (Reactants)

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 The substances that undergo chemical change in the above reaction i.e. magnesium and oxygen, are the reactants. The new substance, magnesium oxide, formed during the reaction is the product.

What is a word-equation?  A chemical reaction written in words showing change of reactants to products by an arrow placed between them is called a word equation. The reactants are written on the left-hand side (LHS) with a plus sign (+) between them if they are more than one. Similarly, products are written on the right-hand side (RHS) with a plus sign (+) between them if they are more than one. The arrowhead points towards the products, and shows the direction of the reaction.

Writing a Chemical Equation:  A chemical equation represents a chemical reaction and is written using symbols for element and formulae for compounds. The reaction of magnesium with oxygen to form magnesium oxide can be written as 2Mg + O2 → 2MgO  The number of atoms of each element on the LHS and RHS of the arrow must be the same on both the sides. If not, then the equation is unbalanced as the mass of the elements is not the same on both sides of the equation.

Balancing Chemical Equations: 

The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. That is, the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants. The number of atoms of each element remains the same, before and after a chemical reaction. Hence, we need to balance a chemical equation. The word–equation for the reaction of zinc with sulphuric acid is Zinc + Sulphuric acid → Zinc sulphate + Hydrogen  The above word-equation may be represented by the following chemical equation, Zn + H2SO4 → ZnSO4 + H2  Let us count the number of atoms of different elements on both sides of the arrow. Number of atoms in Number of atoms in Element reactants (LHS) products (RHS) Zn

1

1

H

2

2

S

1

1

O

4

4



As the number of atoms of each element is the same on both sides of the arrow. The above equation is a balanced chemical equation. Let us try to balance the following chemical equation, Fe + H2O → Fe3O4 + H2  Step I: List the number of atoms of different elements present in the unbalanced equation Number of atoms in Number of atoms in Element reactants (LHS) products (RHS)

2

Fe

1

3

H

2

2

O

1

4


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

Step II: Start balancing with the compound that contains the maximum number of atoms. It may be a reactant or a product. We select Fe3O4 and the element oxygen in it. There are four oxygen atoms on the RHS and only one on the LHS.  To balance the oxygen atoms: Atoms of oxygen In reactants In products Initial

1(in H2O)

4 (in Fe3O4)

4 1×4  To equalise the number of atoms, we cannot alter the formulae of the compounds or elements involved in the reactions. For example, to balance oxygen atoms we can put coefficient ‘4’ as 4H2O and not H2O4 or (H2O)4. Now the partly balanced equation becomes: [partly balanced equation] Fe + 4H2O → Fe3O4 + H2  Step III: Fe and H atoms are still not balanced. Let us balance hydrogen atoms in the partly balanced equation. To equalise the number of H atoms, make the number of molecules of hydrogen as four on the RHS. Atoms of hydrogen In reactants In products To balance

Initial

8(in 4 H2O)

2(in H2)

8

2×4

To balance 

The equation would be, [partly balanced equation] Fe + 4 H2O → Fe3O4 + 4 H2  Step IV: Now balance Fe in the equation. Atoms of iron In reactants In products Initial To balance  







1 (in Fe)

3(in Fe3O4)

1×3

3

To equalise Fe, we take three atoms of Fe on the LHS. [balanced equation] 3Fe + 4H2O → Fe3O4 + 4 H2 The number of atoms of elements on both sides of the equation are equal. This equation is now balanced. This method of balancing chemical equations is called hit-and-trial method as we make trials to balance the equation by using the smallest whole number coefficient. Step V: Finally, to check the correctness of the balanced equation, we count atoms of each element on both sides of the equation. 3Fe + 4H2O → Fe3O4 + 4H2. Step VI: Writing Symbols of Physical States: To make a chemical equation more informative, the physical states of the reactants and products are mentioned along with their chemical formulae. The gaseous, liquid, aqueous and solid states of reactants and products are represented by the notations (g), (l), (aq) and (s) respectively. The word aqueous (aq) is written if the reactant or product is present as a solution in water. The balanced equation above becomes 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g) Sometimes the reaction conditions, such as temperature, pressure, catalyst etc., for the reaction are indicated above and/or below the arrow in the equation. For example: 340 atm CO(g) + 2H2(g)  → CH3OH(l)

Sunlight 6CO2(aq) + 6H2O(l)  → C6H12O6(aq) + 6O2(aq) Chlorophyll

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Types of Chemical Reactions:  We have learnt in Class IX that during chemical reactions atoms of one element do not change into those of another element. Nor do atoms disappear from the mixture or appear from elsewhere, chemical reactions involve the breaking and making of bonds between atoms to produce new substances.  Chemical change or chemical reaction is always associated with change in energy.  In a reaction where a large amount of heat is evolved the reaction mixture is warm. Reactions in which heat is released along with the formation of products are called exothermic chemical reactions.  Examples of exothermic reactions are:  Burning of natural gas, CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + heat  Respiration is an exothermic process.  We all know that we need energy to stay alive and work. We get this energy from the food we eat. During digestion, food is broken down into simpler substances.  For example, rice, potatoes and bread contain carbohydrates. Carbohydrates are broken down to form glucose. This glucose combines with oxygen in the cells of our body and provides energy. The special name of this reaction is respiration. C6H12O6(aq) + 6O2(aq) → 6CO2(aq) + 6H2O(l) + energy (Glucose)

 The decomposition of vegetable matter into compost is also an example of an exothermic reaction.  Reactions in which energy is absorbed are known as endothermic reactions.  Examples of endothermic reactions are:  Reaction of barium hydroxide with ammonium chloride to give barium chloride and ammonium hydroxide.  Calcium carbonate on heating breaks up into calcium oxide and carbon dioxid

Combination Reaction:  Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat. CaO(s) + H2O(l) → Ca(OH)2(aq) (Quick lime)

(Slaked lime)

 In this reaction, calcium oxide and water combine to form a single product, calcium hydroxide. Such a reaction in which a single product is formed from two or more reactants is known as a combination reaction. Some more examples of combination reactions are: Burning of coal, C(s) + O2(g) → CO2(g)  Formation of water from H2(g) and O2(g); 2H2(g) + O2(g) → 2H2O(l) 

Decomposition Reaction:  The decomposition reactions require energy either in the form of heat, light or electricity for breaking down the reactants.  Splitting of the compounds by heat energy is called thermal decomposition. 

Heat 2FeSO4(s)  → Fe2O3(s) + SO2(g) + SO3(g)

(Ferrous sulphate) 

4

(Ferric oxide)

In this reaction you can observe that a single reactant breaks down to give simpler products. This is a decomposition reaction. Ferrous sulphate crystals (FeSO4⋅7H2O) lose Universal Tutorials – X CBSE (2012–13) – Chemistry

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water when heated and the colour of the crystals changes. It then decomposes to ferric oxide (Fe2O3), sulphur dioxide (SO2) and sulphur trioxide (SO3). Ferric oxide is a solid, while SO2 and SO3 are gases.  Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating is an important decomposition reaction Heat CaCO3(s)  → CaO(s) + CO2(g)

(Limestone) 

(Quick lime)

Another example of a thermal decomposition reaction is Heat 2Pb(NO3)2(s)  → 2PbO(s) +

(Lead nitrate)

4NO2(g)

+ O2(g)

(Lead oxide) (Nitrogen oxide) (Oxygen)

 Splitting of a compound by light energy is called photochemical reaction.  White silver chloride turns grey in sunlight. This is due to the decomposition of silver chloride into silver and chlorine by light. Sunlight 2AgCl(s)  → 2Ag(s) + Cl2(g)



Silver bromide also behaves in the same way. Sunlight 2AgBr  → 2Ag(s) + Br2(g)

 The above reactions are used in black and white photography.  Decomposition brought about by electrical energy is known as electrolytic decomposition or electrolysis. 

electric current 2H2O(l)   → 2H2↑ + O2↑

(acidified water)

Displacement Reaction:  Consider the reaction, Fe + CuSO4 → FeSO4 + Cu  The iron nail become brownish in colour and the blue colour of copper sulphate solution fades  In this reaction, iron has displaced or removed another element copper, from copper sulphate solution. This reaction is known as a displacement reaction.  Other examples of displacement reactions are →

Zn(s) + CuSO4(aq) (Copper sulphate)

→

Pb(s) + CuCl2(aq) (Copper chloride)

ZnSO4(aq) + Cu(s) (Zinc sulphate)

PbCl2(aq) + Cu(s) (Lead chloride)

 As zinc and lead are more reactive elements than copper. They displace copper from its compounds.  A chemical reaction in which less reactive atom or group of atoms is displaced by another more reactive atom or group of atoms to form a new substance is called a displacement reaction.

Double Displacement Reaction:  In the reaction below Na2SO4(aq) + (Sodium sulphate)

BaCl2(aq) (Barium chloride)

→

BaSO4(s)

+

(Barium sulphate) (insoluble)

2NaCl(aq) (Sodium chloride) (soluble)

 A white substance, which is insoluble in water, is formed. This insoluble substance formed is known as a precipitate. Any reaction that produces a precipitate can be called a precipitation reaction. A double displacement reaction always produces a precipitate.  The white precipitate of BaSO4 is formed by the reaction of SO 24− and Ba . The other product formed is sodium chloride which remains in the solution (soluble) 2+

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 A chemical reaction in which the cations of two compounds mutually exchange places to form two new compounds one of which is a precipitate is called a double displacement reaction.

Oxidation and Reduction Reactions: Heat  In this reaction, 2Cu + O2  → 2CuO

 The surface of copper powder becomes coated with black copper (II) oxide. This is because oxygen is added to copper and copper oxide is formed. If hydrogen gas is passed over this heated material (CuO), the black coating on the surface turns brown as the reverse reaction takes place and copper is obtained. Heat CuO + H2  → Cu + H2O

 If a substance gains oxygen during a reaction, it is said to be oxidised. If a substance loses oxygen during a reaction, it is said to be reduced. During the above reaction the copper(II) oxide is losing oxygen and is being reduced. The hydrogen is gaining oxygen and is being oxidised. In other words, one reactant gets oxidised while the other gets reduced during a reaction. Such reactions are called oxidation-reduction reactions or redox reactions. Oxidation Heat CuO + H2  → Cu + H2O

Reduction  Some other examples of redox reactions are: Oxidation i)

Heat ZnO + C  → Zn + CO

Reduction

Oxidation ii)

MnO2 + 4HCl → MnCl2 + 2H2O + Cl2 Reduction

 In the first reaction carbon is oxidised to CO and ZnO is reduced to Zn. In the second reaction HCl is oxidised to Cl2 whereas MnO2 is reduced to MnCl2. From the above examples we can say that if a substance gains oxygen or loses hydrogen during a reaction, it is oxidised. If a substance loses oxygen or gains hydrogen during a reaction, it is reduced.  Oxidation reaction in everyday life:  Iron articles are shiny when new, but get coated with a reddish brown powder when left for some time. This process is commonly known as rusting of iron. Some other metals also get tarnished in this manner.  When a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion.  The black coating on silver and the green coating on copper are other examples of corrosion.  Corrosion causes damage to car bodies, bridges, iron railings, ships and to all objects made of metals, especially those of iron. Corrosion of iron is a serious problem. Every year an enormous amount of money is spent to replace damaged iron.  When fats and oils are oxidised, they become rancid and their smell and taste changes. Usually substances which prevent oxidation (antioxidants) are added to foods containing fats and oils. Keeping food in air tight containers helps to slow down oxidation.

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APPENDIX: NCERT ACTIVITIES Activity 1.1 (Experiment): Aim: To show the reaction between magnesium and Tongs oxygen present in the air. Magnesium ribbon Apparatus: Mg ribbon, watch – glass, pair of tongs, burner, sand paper Procedure: Clean a magnesium ribbon about 2 cm Burner Watch glass Magnesium long by rubbing it with sandpaper. Hold it with a pair oxide of tongs Burn it using a burner and collect the ashes so formed in a watch – glass as shown in the fig. while burning the magnesium ribbon keep it as far as possible from your eyes. Observation: magnesium ribbon burns with a dazzling white flame and changes into a white powder. This powder is magnesium oxide Conclusion: MgO is formed due to the reaction between magnesium and oxygen present in the air. Equation, 2Mg + O2 → 2MgO Activity 1.2 (Experiment): Aim: To show change in state and colour when a chemical reaction takes place. Apparatus: lead nitrate solution, potassium iodide solution, test tube, and a conical flask. Procedure: Take lead nitrate solution in a test tube Add potassium iodide solution to this. Observation: lead nitrate reacts with potassium iodide to give lead iodide and potassium nitrate. The colour of the products is different from that of the reactants. Conclusion: Pb(NO3)2 + 2KI → PbI2 + 2KNO3. The change in colour is because lead iodide and potassium nitrate have been formed after the reaction. PbI2 is a yellow ppt. KNO3 is a colourless solution. Activity 1:3 (Experiment): Aim: To show the interaction between zinc granules and hydrochloric acid or sulphuric acid (formation of H gas) Apparatus: Zinc granules, conical flask, test tube, hydrochloric acid / sulphuric acid Procedure: Take a few zinc granules in a conical flask or a test tube. Add dilute hydrochloric acid or sulphuric acid to this. Touch the conical flask or test tube. Observation: A gas is evolved and the conical flask is warm Conclusion: From this we conclude that when a chemical reaction takes place there is a change in the state, colour, and temperature. Zn + H2SO4 → ZnSO4 + H2↑ + heat Zn + 2HCl → ZnCl2 + H2↑ + heat Activity 1.4 (Experiment): Aim: Formation of slaked lime by the reaction of calcium oxide with water Apparatus: Calcium oxide, beaker, and water Procedure: Take a small amount of calcium oxide or quick lime in a beaker. Slowly add water to this. Touch the beaker Observation: The beaker becomes hot (exothermic reaction). It reacts vigorously with water. Conclusion: Slaked lime is formed by the reaction of the combination of calcium oxide with water Ca(OH)2(aq) + heat CaO(s) + H2O(l) → (quick lime)

(Slaked lime) (exothermic reaction)

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Activity 1.5 (Experiment): Wafting gas gently Aim: To show a decomposition reaction towards nose Apparatus: ferrous sulphate crystals, dry boiling tube and burner Procedure: Take about 2g ferrous sulphate crystals in a dry boiling tube. Note the colour of the ferrous Do not point sulphate crystals. Heat the boiling tube over the flame the mouth of tube of a burner or spirit lamp observe the colour of the boiling at your neighbours or yourself crystals after heating Burner Observation: The green colour of the ferrous sulphate crystals has changed there is also the characteristic odour of burning sulphur. Conclusion: This is a Decomposition reaction, shown by the reaction

Boiling tube Ferrous sulphate crystals

Heat 2FeSO4(s)  → Fe2O3 + SO2(g) + SO3(g)

Activity 1.6 (Experiment): Aim: Heating of lead nitrate and emission of nitrogen dioxide Apparatus: lead nitrate powder, boiling tube, pair of tongs and burner Procedure: Take about 2 g lead nitrate powder in a boiling tube. Hold the boiling tube with a pair of tongs and heat it over a flame. Observe the change if any. Observation: We observe the emission of brown fumes. Conclusion: These fumes are of nitrogen dioxide (NO2). The reaction that takes place is Heat 2Pb(NO3)2(s)  → 2PbO(s)

(Lead nitrate)

(Lead oxide)

+

4NO2(g)

(Nitrogen dioxide)

+

Test tube holder Boiling tube Lead nitrate

Burner

O2(g) (Oxygen)

Activity 1.7 (Experiment): Plastic mug Aim: To show that water is a compound Hydrogen Oxygen containing two atoms of hydrogen and 1 atom of oxygen Test tube Apparatus: Plastic mug, rubber stoppers, Water carbon electrodes, 6 volt battery, water, dilute sulphuric acid, burning candle Water Graphite rod Procedure: Take a plastic mug. Drill two holes Rubber stopper at its base and fit rubber stoppers in these Cathode Anode holes. Insert carbon electrodes in these rubber stoppers as shown in fig then connect these 6V Switch Battery electrodes to a 6 volt battery. Fill the mug with water such that the electrodes are immersed. Add a few drops of dilute sulphuric acid to the water. Take two test tubes filled with water and invert them over the two carbon electrodes. Switch on the current and leave the apparatus undisturbed for some time. Observe the formation of bubbles at both the electrodes. These bubbles displace water in the test tubes. The volume of the gas collected is not the same in both the test tubes. Once the test tubes are filled with the respective gases, remove them carefully. Test these gases one by one by bringing a burning candle close to the mouth of the test tubes. Observation: We observe the formation of bubbles at both the electrodes. These bubbles displace water in the test tubes. The volume in one test tube is twice that in the other test tube. The test tube containing hydrogen gas has double the volume of the test tube containing oxygen gas. Hydrogen gas burns with a light blue flame with a pop sound. Conclusion: Water is a compound containing two atoms of hydrogen and 1 atom of oxygen. 8


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Activity 1.8 (Experiment): Aim: To show how silver chloride is affected by sunlight Apparatus: silver chloride and a china dish. Sunlight Procedure: Place this china dish containing silver chloride in sunlight for some time. Observe the colour of the silver chloride China dish after some time. Silver chloride Observation: White silver chloride turns grey in sunlight. Conclusion: This is due to the decomposition of silver chloride into silver and chlorine by light Sunlight 2AgCl(s)  → 2Ag(s) + Cl2(g)

Activity 1.9 (Experiment): Aim: To show displacement reaction Apparatus: two iron nails, sand paper, copper sulphate solution, thread and two test tubes. Procedure: Take two iron nails and clean them by rubbing them with sand paper. Take two test tubes marked as (A) and (B). In each test tube, take about 10 ml copper sulphate solution. Tie one iron nail with a thread and immerse it carefully in the copper sulphate solution in test tube A for about 20 minutes. Keep one iron nail aside for comparison. After 20 minutes, take out the iron nail from the copper sulphate solution. Compare the intensity of the blue colour of copper sulphate solutions in the test tubes (A) and (B). Also, compare the colour of the iron nail dipped in the copper sulphate solution with the one kept aside. Observation: the iron nail dipped in the copper sulphate solution in test tube A becomes brownish in colour and the blue colour of copper sulphate solution fades in test tube A. While the blue colour of copper sulphate solution in test tube B remains the same. Conclusion: iron has displaced or removed another element, copper, from copper sulphate solution in test tube A. This reaction is known as displacement reaction. Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s) [copper sulphate]

[Iron sulphate]

Stand

Test tube

Iron nail

Iron nail taken out from copper Sulphate solution

Copper Sulphate Solution (test tube A)

Test tube stand

Test tube Thread Copper sulphate solution Iron nail

Reaction Mixture (test tube B)

Activity 1.10 (Experiment): Aim: To show double displacement reaction Apparatus: 3 ml of sodium sulphate, 2 test tubes, 3 ml of Test tube barium chloride solution. containing solution of sodium sulphate Procedure: Take about 3 ml of sodium sulphate solution in a test tube. In another test tube, take about 3 ml of barium chloride solution, Mix the two solutions. Test tube Observation: A white substance, which is insoluble in water, containing solution is formed. This insoluble substance formed is known as a of barium chloride precipitate. Any reaction that produces a precipitate can be called a precipitation reaction. Conclusion: This is a double displacement reaction shown by + +2 +2 the equation below where Na being more reactive than Ba displaces Ba from its compound BaCl2 and takes its place to form NaCl. + BaCl2(aq) → BaSO4(s) + 2NaCl(aq) Na2SO4(aq) (sodium sulphate)

Volume

(Barium chloride)

(Barium sulphate)

(Sodium chloride)


9

10

Activity 1.11 (Experiment): Aim: To show oxidation and reduction reaction China dish containing130 Apparatus: China dish 1g copper powder, burner, Wire gauz copper powder wire gauze, tripod stand and Hydrogen gas. Tripod stand Procedure:  Heat a china dish containing about 1 g copper Burner powder.  Now pass hydrogen gas over this heated material. Observation:  The surface of copper powder becomes coated with black copper oxide.  Hydrogen gas is passed over this heated material [CuO] the black coating on the surface turns brown as the reverse reaction takes place and copper is obtained. Conclusion: In the first case copper, was oxidized to copper oxide by the following reaction Heat 2Cu + O2  → 2CuO this is an oxidation reaction (black coating)

In the second case when hydrogen gas was passed over heated [CuO] copper metal was obtained because copper oxide got reduced to copper metal by the following reaction Heat CuO + H2  → Cu + H2O

REVIEW QUESTIONS: CW Exercise: 1) Balance the following reactions wherever required. a) SO2 + H2O → H2SO3 c) Na2O + H2O → NaOH e) NaOH + HCl [dil.] → NaCl + H2O

b) SO3 + H2O → H2SO4 d) K + H2O → KOH + H2 f) Zn + HCl [dil.] → ZnCI2 + H2

< 200°C g) NaCl + H2SO4 (conc.)  → NaHSO4 + HCl > 200°C h) NaNO3 + H2SO4 (conc.)  → Na2SO4 + HNO3 2) Translate the reactions into word equations after balancing them

< 200°C a) NaCl + H2SO4 (conc.)  → NaHSO4 + HCl(g) > 200°C b) NaCl + H2SO4 (conc.)  → Na2SO4 + HCl(g)

>500° C

H2 + Cl2 d) NH3 + HCl(g) → NH4Cl c) HCl(g) f) Fe + HCl(g) → FeCl2 + H2 e) Zn + HCl(g) → ZnCl2 + H2 h) CaO + HCl [dil.] → CaCl2 + H2O g) Mg + HCl [dil.] → MgCl2 + H2 j) Na2CO3 + HCl [dil.] → NaCl + H2O + CO2 i) NH4OH + HCl [dil.] → NH4Cl + H2O 3) Write balanced equations for the following reactions and identify the types of reactions. a) CuO + H2SO4 [dil.] → ______ + H2O c) Fe + Cl2 → _____

b) Fe + H2SO4 [dil.] → _____ + H2 d) Pb(NO3)2 + NaCl → _____ + _____

e) CaCl2 + Na2CO3 → _____ + _____

< 400°C f) ZnCO3  → ZnO + CO2

∆ g) Al2O3 . 2H2O + Na2CO3 → NaAlO2 + H2O + CO2 1100°C h) Al(OH)3  → Al2O3 + H2O j) CO2 + C → CO – ∆

10

i) C + O2 → CO2 + ∆ k) CaCO3 → CaO + CO2 – ∆


Volume


11

HW Exercise: 1) Balance the following reactions wherever required. a) NaHCO3 + H2SO4 [dil.] → Na2SO4 + H2O + CO2 b) Na2CO3 + H2SO4 [dil.] → Na2SO4 + H2O + CO2 c) Cu(OH)2 + Na2SO4 [dil.] → CuSO4 + NaOH d) Al(s) + H2O → Al2O3(s) + H2(g) f) Fe + Cl2 → FeCl3 e) Fe + H2SO4 (dil.) → FeSO4 + H2 g) Zn + S → ZnS h) Pb(NO3)2 + NaCl → NaNO3 + PbCl2 i) CaCl2 + Na2CO3 → NaCl + CaCO3 2) Translate the reactions into word equations after balancing them a) NaHCO3 + HCl [dil.] → NaCl + H2O + CO2

Heat b) NaHCO3  → Na2CO3 + H2O + CO2

c) NaHSO3 + HCl [dil.] → NaCl + H2O + SO2 d) FeS + HCl [dil.] → FeCl2 + H2S f) Pb(NO3)2 + HCl [dil.] → PbCl2↓ + HNO3 e) AgNO3 + HCl [dil.] → AgCl↓ + HNO3 g) MnO2 + HCl [conc.] → MnCl2 + H2O + Cl2 h) PbO2 + HCl [conc.] → PbCl2 + H2O + Cl2 i) Pb3O4 + HCl [conc.] → PbCl2+ H2O + Cl2 3) Write balanced equations for the following reactions and identify the types of reactions. a) CaO + SiO2 → CaSiO3 c) Zn + O2 → ZnO e) Zn + NaOH → Na2ZnO2 + H2 g) Fe + O2 → Fe3O4

b) Fe2O3 + CO → Fe + CO2 d) Zn + S → ZnS f) Zn + H2SO4 [dil.] → ZnSO4 + H2 h) Fe + H2O  Fe3O4 + H2

i) Fe + Cl2 → FeCl3

j) Fe + S → FeS NCERT EXERCISE:

1) Why does the colour of copper sulphate solution change when an iron nail is dipped in it? 2) Give an example of a double displacement reaction other than the one given in the notes. 3) Identify the substances that are oxidised and the substances that are reduced in the following reactions. i) 4Na(s) + O2(g) → 2Na2O(s) ii) CuO(s) + H2(g) → Cu(s) + H2O(l) 4) Why should a magnesium ribbon be cleaned before burning in air? 5) Write a balanced equation for the following chemical reactions. i) Hydrogen + Chlorine → Hydrogen chloride ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride iii) Sodium + Water → Sodium hydroxide + Hydrogen 6) Write a balanced chemical equation with state symbols for the following reactions. i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride. ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water. 7) A solution of a substance ‘X’ is used for white washing. i) Name the substance ‘X’ and write its formula. ii) Write the reaction of the substance ‘X’ named in (i) above with water. 8) Why is the amount of gas collected in one of the test tubes in the decomposition of water double the amount collected in the other? Name this gas.

Volume


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12

Which of the statements about the reaction below are incorrect? 9) 2PbO(s) + C(s) → 2Pb(s) + CO2(g) a) Lead is getting reduced b) Carbon dioxide is getting oxidised c) Carbon is getting oxidized d) Lead oxide is getting reduced i) (a) and (b) ii) (a) and (c) iii) (a), (b) and (c) iv) all 10) Fe2O3 + 2Al → Al2O3 + 2Fe. The above reaction is an example of a a) combination reaction b) double displacement reaction c) decomposition reaction d) displacement reaction 11) What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer. a) Hydrogen gas and iron chloride are produced b) Chlorine gas and iron hydroxide are produced c) No reaction takes place d) Iron salt and water are produced 12) What is a balanced chemical equation? Why should chemical equations be balanced? 13) Translate the following statements into chemical equations and then balance them. a) Hydrogen gas combines with nitrogen to form ammonia b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas 14) Balance the following chemical equations, if necessary. a) HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O b) NaOH + H2SO4 → Na2SO4 + H2O d) BaCl2 + H2SO4 → BaSO4 + HCl c) NaCl + AgNO3 → AgCl + NaNO3 15) Write chemical equations for the following reactions. Balance them if required. a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water b) Zinc + Silver nitrate → Zinc nitrate + Silver c) Aluminium + Copper chloride → Aluminium chloride + Copper d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride 16) Write the balanced chemical equation for the following and identify the type of reaction in each case. a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s) b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g) c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g) d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g) 17) What does one mean by exothermic and endothermic reactions? Give examples. 18) Why is respiration considered an exothermic reaction? Explain. 19) Why are decomposition reactions called the opposite of combination reactions? 20) Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity. 21) What is the difference between displacement and double displacement reactions? Write equations for these reactions. 22) In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved. 23) What do you mean by a precipitation reaction? Explain by giving examples. 24) Explain the following in terms of gain or loss of oxygen with two examples each. a) Oxidation b) Reduction 12


Volume


13

25) A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed. 26) Why do we apply paint on iron articles? 27) Oil and fat containing food items are flushed with nitrogen. Why? 28) Explain the following terms with one example each: a) Corrosion b) Rancidity MULTIPLE CHOICE QUESTIONS: PRACTICAL (THEORY) 1) When CuSO4 reacts with Fe the product formed will be: a) FeSO4 b) Fe2(SO4)3 c) Fe d) FeS 2) The substance which loses electrons is called as: a) Oxidising agent b) Reducing agent c) Catalyst d) None of these 3) Which of the following reactions is a double displacement reaction? a) Zn + CuSO4 → ZnSO4 + Cu b) NaOH + HCl → NaCl + H2O d) CaO + H2O → Ca(OH)2 c) CaCO3 → CaO + CO2 4) An arrow pointing downwards in an equation indicates: a) Evolution of gas b) Formation of precipitate c) An aqueous solution d) Both (a) and (b) 5) Name one compound of hydrogen which is very essential for existence of life on the earth + a) H2O b) H2O2 c) CH4 d) H3O 6) Find X in the reaction, Zn + H2SO4 → X + H2 a) ZnS b) ZnSO4 c) ZnO d) ZnSO3 7) Which one of the following is a decomposition reaction? a) Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s) b) BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq) d) C(s) + O2(g) → CO2(g) c) CaCO3(s) → CaO(s) + CO2(g) heat

8) CaCO3 → CaO + CO2. This reaction is an example of: a) Electrolysis b) Thermal decomposition c) Displacement d) Combination 9) Which of the following is not a chemical reaction? a) Souring of milk b) Rusting of iron c) Dissolution of sugar in water d) Digestion of food in our body 10) a Mg3N2 + b H2O → c Mg(OH)2 + d NH3. When the equations is balanced, the coefficients a, b, c, d respectively are a) 1, 3, 3, 2 b) 1, 6, 3, 2 c) 1, 2, 3, 2 d) 2, 3, 6, 2 11) Which of the following reaction has not been correctly represented? a) BaCI2(aq) + H2S04(aq) → BaSO4↓ + 2 HCl

b) Zn(s) + H2SO4(aq) → ZnSO4↓ + H2(g)

c) C(s) + O2(g) → CO2(g) + Heat

heat d) 2KCIO3(s)  → 2 KCI(s) + 3O2↑

12) Which of the following is not a combination reaction? a) Fe + S → FeS

b) CaO + CO2 → CaCO3

c) NH3 + HCI → NH4Cl d) AgNO3 + NaCI → AgCI + NaNO3 13) Which of the following is not a thermal decomposition reaction? a) 2H2O → 2 H2 + O2

b) 2 FeSO4 → Fe2O3 + SO2 + SO3

c) ZnCO3 → ZnO + CO2

d) 2 KClO3 → 2 KCI + 3 O2

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14

14) Which of the following reactions will not occur? a) Mg + H2SO4 → MgSO4 + H2

b) Cu + H2SO4 → CuSO4 + H2

c) 2 Al + 6 HCl → 2 AICl3 + 3 H2 d) Fe + 2 HCl → FeCI2 + H2 15) Which of the following reactions will occur? a) 2 Ag + Cu(NO3)2 → 2 AgNO3 + Cu

b) Cu + ZnSO4 → CuSO4 + Zn

c) 2 Ag + H2SO4 → Ag2SO4 + H2

d) 2 Al + 3 FeSO4 → Al2(SO4)3 + 3 Fe

16) In the reaction, 2H2S + SO2 → 3S + 2H2O a) H2S has been oxidized b) SO2 has been oxidized d) SO2 is the reducing agent c) H2S is the oxidizing agent 17) Which of the following reactions is a redox reaction as well as a displacement reaction? a) 2 HgCI2 + SnCl2 → Hg2CI2 + SnCI4

b) ZnO + C → Zn + CO

c) 2 Al + 6 HCI → 2 AlCl3 + 3 H2 d) H2S + Cl2 → 2 HCI + S 18) The correct formula of rust is b) Fe3O4 c) Fe2O3 . x H2O d) Fe3O4 . x H2O a) Fe2O3 19) Galvanisation of iron means coating iron with a) Chromium b) Nickel c) Zinc d) Tin 20) Which of the following metals is protected by a layer of its oxide? a) Copper b) Silver c) Iron d) Aluminium 21) The term ‘rancidity’ represents a) Acid rain b) Oxidation of fatty food c) Rotting of fruit d) Fading of coloured clothes in the sun ANSWERS: CW Exercise: 1) c) Na2O + H2O → 2NaOH f) Zn + 2HCl(dil) → ZnCl2 + H2

d) 2K + 2H2O → 2KOH + H2

> 200°C 2) b) 2NaCl + H2SO4 (conc.)  → Na2SO4 + 2HCl(g)

e) Zn + 2HCl(g) → ZnCl2 + H2 g) Mg + 2HCl [dil.] → MgCl2 + H2 j) Na2CO3 + 2HCl [dil.] → 2NaCl +H2O +CO2 3) a) CuO + H2SO4 [dil.] → CuSO4+ H2O b) Fe + H2SO4 [dil.] → FeSO4+ H2 c) Fe + Cl2 → FeCl2 d) Pb(NO3)2 + 2NaCl → PbCl2 + 2NaNO3 e) CaCl2 + Na2CO3 → CaCO3 + 2NaCl < 400°C f) ZnCO3  → ZnO + CO2

f) Fe + 2HCl(g) → FeCl2 + H2 h) CaO + 2HCl [dil.] → CaCl2 + H2O [Neutralization]; double displacement. [simple displacement] [Direct combination] [Double displacement] [Double displacement] [Decomposition]

∆

g) Al2O3 . 2H2O + Na2CO3 → 2NaAlO2 + 2H2O + CO2 [displacement and combination]

14

1100°C h) 2Al(OH)3  → Al2O3 + 3H2O

[Decomposition]

i) C + O2 → CO2 + ∆ j) CO2 + C → 2CO – ∆

[Combination and oxidation] [Combination and reduction]

∆ CaO + CO2 – ∆ k) CaCO3 →

[Decomposition and endothermic]


Volume


15

HW Exercise: 1) a) 2NaHCO3 + H2SO4 [dil.] → Na2SO4 + 2H2O + 2CO2 c) Cu(OH)2 + Na2SO4 [dil.] → CuSO4 + 2NaOH f) 2Fe + 3Cl2 → 2FeCl3 d) 2Al(s) + 3H2O → Al2O3(s) + 3H2(s) i) CaCl2 + Na2CO3 → 2NaCl + CaCO3 h) Pb(NO3)2 + 2NaCl → 2NaNO3 + PbCl2 Heat 2) b) 2NaHCO3  → Na2CO3 + H2O + CO2 f) Pb(NO3)2 + 2HCl [dil.] → PbCl2↓ + 2HNO3 h) PbO2 + 4HCl [conc.] → PbCl2 + 2H2O + Cl2 3) a) CaO + SiO2 → CaSiO3 b) Fe2O3 + 3CO → 2Fe + 3CO2 c) 2Zn + O2 → 2ZnO d) Zn + S → ZnS e) Zn + NaOH → Na2ZnO2 + H2 f) Zn + H2SO4 [dil.] → ZnSO4 + H2 g) 3Fe + 2O2 → Fe3O4 h) 3Fe + 4H2O  Fe3O4 + 4H2

d) FeS + 2HCl [dil.] → FeCl2 + H2S g) MnO2 + 4HCl [conc.] → MnCl2 +2H2O +Cl2 i) Pb3O4 + 8HCl [conc.] → 3PbCl2+ 4H2O + Cl2 [Combination] [Reduction – oxidation] [Combination and oxidation] [Combination] [Combination and displacement] [Displacement] [Combination] [Redox]

i) 2Fe + 3Cl2 → 2FeCl3 [Combination] j) Fe + S → FeS [Combination] NCERT Exercise: 1) Displacement reaction 2) CaCl2 + MgSO4 → CaSO4 + MgCl2 3) (i) Na oxidized, (ii) CuO is reduced, H2 is oxidized to water. 4) Mg gets oxidized to MgO when exposed to air at ordinary temperature. Hence it has to be cleaned / brushed to get Mg. 5) (i) H2 + Cl2 = 2HCl (ii) 3BaCl2 + Al2(SO4)3 → 3BaSO4 + 2AlCl3 (iii) 2Na + 2H2O → 2NaOH + H2 6) (i) BaCl2(aq) + Na2SO4(aq) → BaSO4(s)↓ + 2NaCl(aq) (ii) NaOH(aq) + HCl(aq) → NaCl(l) + H2O(l) 7) i) Calcium oxide, CaO ii) CaO + H2O → Ca(OH)2 8) Water consists of two parts of H2 and one part of O2. Hence the above statement the gas whose quantity is double is hydrogen. 9) 1 10) d 11) a b) 2H2S + 3O2 → 2H2O + 2SO2 13) a) 3H2 +N2 → 2NH3 d) 2K + 2H2O → 2KOH + H2↑ c) 3BaCl2 + Al2(SO4)3 → 3BaSO4↓ + 2AlCl3 b) 2NaOH + H2SO4 → Na2SO4 + 2H2O 14) a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O d) BaCl2 + H2SO4 → BaSO4 + 2HCl c) NaCl + AgNO3 → AgCl + NaNO3 b) Zn + 2AgNO3 → Zn(NO3)2 + 2Ag 15) a) Ca(OH)2 + CO2 → CaCO3 + H2O c) 2Al + 3CuCl2 → 2AlCl3 + 3Cu d) BaCl2 + K2SO4 → BaSO4 + 2KCl [double displacement] 16) a) 2KBr + BaI2 → 2KI + BaBr2 [decomposition] b) ZnCO3 → ZnO + CO2 [Combination] c) H2 + Cl2 → 2HCl [displacement] d) Mg(s) + 2HCl (aq) → MgCl2(aq) + H2(g)↑ 22) 2AgNO3 + Cu → Cu(NO3)2 + 2Ag↓ 24) a) gaining of O2 or loss of H2 b) loss of O2 or gaining of H2 25) X = Cu; black color CuO 26) To prevent rusting/ oxidation of Fe Note: Not all questions have been solved from the exercises behind the chapter. Students are expected to answer these questions on their own on completion of the chapter. Volume


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16

Chapter 02: Acids, Bases and Salts Chapter Map: → Chemical properties of Acids and Bases → Acids and Bases in the Laboratory → How do Acids and Bases react with Metals? → Reaction of Acids with Metal Carbonates and Metal Hydrogencarbonates → Reaction of Acids and Bases with each other → Reaction of Metallic oxides with Acids → Reaction of Non–metallic Oxides with Bases → Common properties of Acids and Bases → Behaviour of Acids and Bases in water → Strength of Acidic and Basic solutions → pH of solutions → Importance of pH in Everyday Life → Salts → Family of salts → Chemical compounds from Common salt (NaCl, NaOH, CaOCl2, NaHCO3, Na2CO3.10H2O) → Crystals of salts are not dry → Plaster of Paris

What is an acid? 

An acid is a compound which on dissolving in water gives hydronium ions as the only positively charged ions.

What is a base? 

Any substance which gives hydroxyl ions on dissolving in water or reacts with acids to form salt and water only or neutralizes an acid is called a base.

Properties of Acids and Bases: Substance Methyl orange Red litmus Blue litmus Phenolphthalein

Acids Reddish orange Red Red Colourless

Bases Yellow Blue Blue Pink

Distinguish between acids and Bases: Acids Sour to taste Corrosive to touch Turn blue litmus red + Produce H ions when mixed with water 16

Bases Bitter to taste Soapy to touch Turn red litmus blue – Produce (OH) ions when mixed with water


Volume

Chapter 02: Acids, Bases and Salts

17

What is litmus solution? 

This solution is a natural indicator. It is neither basic nor acidic its colour is purple. However, this colour changes to red in an acidic medium and to blue in a basic medium.  There are other indicators as well eg Turmeric, methyl orange, methyl red, phenolphthalein.  Some naturally occurring materials like red cabbage leaves, coloured petals of some flowers eg. Hydrangea, Petunia, Geranium also indicate the presence of an acid or a base in a solution.

What is a Salt? 

A salt is an ionic compound containing a positive ion other than hydrogen ion and a negative ion other than a hydroxyl ion.  A salt is a substance having different tastes. It has a mild irritating sensation when touched.

Reaction of Acids with metal carbonates & Metal Hydrogencarbonates: 

Acids react with metal carbonates to give salt, water and CO2. Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)  Acids react with metal hydrogen carbonates to give salt, water and CO2. NaHCO3(s) + HCl(aq) → NaCl(aq) + H2O(l) + CO2(g)

Reaction of metallic oxides with Acids: 

When acids react with metallic oxides a salt and water are formed. This reaction is similar to the reaction when acids and bases react with each other. This proves that metallic oxides are basic in nature. Na2O + 2HCl → 2NaCl + H2O

Reaction of non–metallic oxides with bases: 

When bases react with non–metallic oxides a salt and water are formed. This reaction is similar to the reaction when acids and bases react with each other. This proves that non– metallic oxides are acidic in nature. Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l) (Lime water)

(White precipitate)

Comparative properties of all Acids and Bases:  All Acids generate hydrogen gas on reacting with metals, so hydrogen seems to be common to all acids. Hence, when we pass electricity through an acidic solution the electric current is carried through the solution by ions. + +  Since the cation present in acids is H , this suggests that acids produce hydrogen ions, H (aq), in solution, which are responsible for their acidic properties. –  When we dissolve a base like sodium hydroxide in water; (OH ) ions (anions) are generated in water.  When HCl is added to water the following reaction takes place HCl + H2O → H3O + Cl  The separation of H ions from HCl molecules cannot occur in the absence of water.  Hydrogen ions cannot exist alone, but they exist after combining with water molecules. Thus + + hydrogen ions must always be shown as H (aq) or as an hydronium ion (H3O ). + + –  Acids give H3O or H (aq) ions in water. Now, when a base is dissolved in water, OH ions are generated in water. Bases which are soluble in water are called alkalis. Eg. +

–

+

H O

NaOH(s) 2→ Na H2 O

+ (aq)

Mg(OH)2(s) → Mg Volume

+ OH

2+ (aq)

H O

KOH(s) 2→ K

– (aq)

+ 2O H

+ (aq)

+ OH

– (aq)

– (aq)


17

18

 All bases do not dissolve in water. + –  Now as we have identified that all acids generate H (aq) and all bases generate OH (aq), we can view the neutralisation reaction as follows, Acid + Base → Salt + Water H X + M OH → MX + HOH H (aq) + OH (aq) → H2O(l)  The process of dissolving an acid or a base in water is a highly exothermic one. Care must be taken while mixing concentrated nitric acid or sulphuric acid with water. The acid must always be added slowly to water with constant stirring.  If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating. +

–

What is dilution of an acid or a base? 

Mixing an acid or a base with water results in decrease in the concentration of ions + – (H3O /OH ) per unit volume. Such a process is called dilution and the acid or the base is said to be diluted.

Strength of acidic or basic solutions: 

Acid-base indicators are used to distinguish between an acid and a base. + – On dilution or decreasing the concentration of H or OH ions in solutions, per unit volume we can quantitatively find the amount of these ions present in a solution.  Thus, we judge how strong a given acid or a base is. We can do this by making use of an universal indicator, which is a mixture of several indicators. The universal indicator shows different colours at different concentrations of hydrogen ions in a solution.  A scale for measuring hydrogen ion concentration in a solution, called pH scale has been developed. The ‘p’ in pH stands for ‘potenz’ in German, meaning power. This scale was introduced by Sorensen. 

Definition: 

pH of a solution is defined as the negative logarithm of hydrogen ion concentration or + pH = – log [H ]  If hydrogen ion conc. is expressed as 10 raised to its negative power numerical value then the numerical value written over 10 is called pH of the solution. + –X i.e. if [H ] = 10 then pH = X. + –  Every aqueous solution whether neutral, acidic or basic contains both H and OH ions.  The product of [H ] [OH ] for any solution is always 1 × 10 at 25°C. + –  If H concentration is more, the solution is acidic and if OH concentration is more, the solution is basic.  Thus a convenient scale for pH was devised; termed as pH scale. +

+

0

[H ]

10

pH

0

–1

10

–

–2

10

–14

–3

10

–4

10

–5

10

–6

10

–7

10

–8

10

–9

10

–10

10

–11

10

–12

10

–13

10

–14

10

1 2 3 4 5 6 7 8 9 10 11 12 13 14 + – –7 10 mol / litre In pure water [H ] = [OH ] =  On the pH scale we can measure pH from 0 (very acidic) to 14 (very alkaline). pH should be thought simply as a number which indicates the acidic or basic nature of a solution. Higher the hydronium ion concentration, lower is the pH value. + –7 10 [H ] = + pH = 7(neutral) pH = – (–7) log 10 (pH = –log [H ]) 18


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   

19

Solutions with pH from 0 to 6.9 are acids while solutions with pH from 7.1 to 14 are bases. Solutions with pH 0 to 3 are strong acids while those with pH 4 to 6 are weak acids. Solution with pH 7.1 to 10 are weak bases Solutions with pH 11 to 14 are strong bases. 0

Neutral 7

Acidic nature increasing

Basic nature increasing

14

OH− Increase in H+ ion concentration

Decrease in H+ ion concentration +

–

Variation of pH with the change in concentration of H (aq) and OH (aq) ions Colour of Approx. S. Nature of Universal pH Solution No. substance paper value 1) Saliva (before meals) Green 7 Neutral 2) Saliva (after meals) Red <7 Acidic 3) Lemon juice Red <7 Acidic 4) Colourless aerated drink Red <7 Acidic 5) Carrot juice Red <7 Acidic 6) Coffee Red <7 Acidic 7) Tomato juice Red <7 Acidic 8) Distilled water Green 7 Neutral 9) 1 M NaOH Blue 14 Basic 10) 1 M HCl Red <7 Acidic 1

2

Gastric juice (about 1.2)

3

4

5

6

Lemon juice (about 2.2)

7

8

9

Pure water, blood (7.4)

10

11

12

13

Milk of magnesia (10)

Strong Acids / Weak Acids: 

14

Sodium hydroxide solution (about 14)

Strong acids are those acids, which undergo complete dissociation on dissolving in water and hence release large number of hydrogen ions in aqueous solutions. Eg. HCl, H2SO4

e.g. HCl(aq) → H (aq) + Cl (aq)  Weak acids do not undergo complete dissociation and hence release few hydrogen ions. e.g. Acetic acid, Oxalic acid. +

–

e.g. CH3COOH(aq) → CH3COO

– (aq)

+H

+ (aq)

Strong Bases / Weak Bases: 

Strong bases are those bases, which release large number of hydroxyl ions by undergoing complete dissociation in aqueous solutions. E.g. Sodium hydroxide, potassium hydroxide  Weak bases release few hydroxyl ions, as they do not dissociate completely. E.g. Ammonium Hydroxide.

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Importance of pH in Everyday Life: 

Our body works within the pH range of 7.0 to 7.8. Living organisms can survive only in a narrow range of pH change.  When rain water dissolves SO2 and NO2 gases present in the atmosphere its pH is less than 5.6. This is called acid rain. When this acid rain flows into the rivers and seas it lowers the pH of the water there, thus making aquatic life difficult.

pH of the soil in your backyard: 

Plants require a specific pH range for their healthy growth i.e. between 6.0 – 7.5.

pH in our digestive system: 

Our stomach produces hydrochloric acid. It helps in the digestion and preservation of the food stored in the stomach during digestion of food without harming the stomach. During indigestion the stomach produces too much acid and this causes pain and irritation.  To get rid of this pain, people use bases called antacids. These antacids neutralise the excess acid. Magnesium hydroxide (Milk of magnesia), a mild base, is often used for this purpose.

pH change is the cause of tooth decay: 

Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel, made up of calcium phosphate is the hardest substance in the body.  It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5. Bacteria present in the mouth produce acids by the degradation of sugar and food particles that remain in the mouth after eating.  The best way to prevent this is to clean the mouth after eating food. Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay.

Self defence by animals and plants through chemical warfare: 

Bee-sting leaves an acid; formic acid which causes pain and irritation. Use of a mild base like baking soda on the stung area gives relief. Stinging hair of nettle leaves inject methanoic acid causing burning pain.

More about salts: 

Salts of a strong acid and a strong base are neutral with pH value of 7. On the other hand, salts of a strong acid and a weak base are acidic with pH value less than 7 and those of a strong base and a weak acid are basic in nature, with pH value more than 7.

Chemicals from Common Salt:     

Common salt is formed by the combination of hydrochloric acid and sodium hydroxide solution and is called sodium chloride. This is the salt that is used in food, it is a neutral salt. Seawater contains many salts dissolved in it. Sodium chloride is separated from these salts. Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt. Beds of rock salt were formed when seas of bygone ages dried up. Rock salt is mined like coal. Common salt – A raw material for chemicals. The common salt thus obtained is an important raw material for various materials of daily use, such as sodium hydroxide, baking soda, washing soda, bleaching powder and many more.

Sodium hydroxide: 

20

When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. Universal Tutorials – X CBSE (2012–13) – Chemistry

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Chapter 02: Acids, Bases and Salts 

21

The process is called the chlor-alkali process because of the products formed – chlor for chlorine and alkali for sodium hydroxide. electricity 2NaCl(aq) + 2H2O(l)   → 2NaOH(aq) + Cl2(g) + H2(g)



Chlorine gas is given off at the anode, and hydrogen gas at the cathode. Sodium hydroxide solution is formed near the cathode.  The three products produced in this process are all useful. Figure below shows the different uses of these products.

at Cathode

at Anode

at Cathode Fuels, margarine ammonia for fertilisers

Water treatment, swimming pools, De-greasing metals, soaps and PVC. disinfectants, CFCs. pesticides detergents, paper making, artificial fibres

HYDROCHLORIC ACID For: cleaning steel, ammonium chloride, medicines, cosmetics

BLEACH For: household bleaches, Bleaching fabric

Bleaching Powder:  Formula: CaOCl2  Industrial method of preparation is the action of chlorine on dry slaked lime.

Waste gases

Slaked lime Hopper

Ca(OH)2 + Cl2 → CaOCl2 + H2O  It is also called as chloride of lime

Uses:

Chlorine



Used for bleaching cotton, linen in textiles industry, wood pulp in paper factories  As an oxidizing agent. For disinfecting drinking water.

Bleaching powder

Hasenclever Plant Hasenclever Plant

Baking Soda (Sodium Bicarbonate):  Common Name: Baking Soda Formula: NaHCO3  It is produced using sodium chloride as one of the raw materials. NaCl + H2O + CO2 + NH3

→

NH4Cl

(Ammonium chloride)

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NaHCO3 (Sodium hydrogencarbonate)


21

22

Properties: 

Crystals are white in color, sparingly soluble in water, this solution is alkaline  If solution of sodium hydrogencarbonate is boiled or heated, CO2 is given off. So it is used as baking powder to aerate the dough. 2NaHCO3 Heat → Na2CO3 + H2O + CO2  It is a mild non-corrosive base. The following reaction takes place when it is heated during cooking: heat 2NaHCO3  → Na2CO3 + H2O + CO2

(Sodium hydrogencarbonate) 

(Sodium carbonate)

Sodium hydrogencarbonate has got various uses in the household.

Uses: 

The soda commonly used in the kitchen for making tasty crispy pakoras is baking soda. Sometimes it is added for faster cooking.  As an antacid.  As an additive in food and drinks.  In fire extinguishers. Note: Baking powder contains tartaric acid, which neutralises sodium carbonate and thus prevents the cake from tasting bitter

Uses of sodium hydrogencarbonate (NaHCO3): 

For making baking powder, which is a mixture of baking soda (sodium hydrogencarbonate) and a mild edible acid such as tartaric acid. When baking powder is heated or mixed in water, the following reaction takes place + NaHCO3 + H → CO2 + H2O + Sodium salt of acid (From any acid)



Carbon dioxide produced during the reaction causes the dough for the bread or cakes to rise making them soft and spongy.

Washing soda     

Another chemical that can be obtained from sodium chloride is Na2CO3.10H2O (washing soda). Common name: Washing soda Formula: Na2CO3 . 10 H2O A Molecule of sodium carbonate contains 10 molecules of water of crystallization. Anhydrous sodium carbonate is commonly known as soda ash. Sodium carbonate can be obtained by heating baking soda. On recrystallisation of sodium carbonate we get washing soda. It is also a basic salt. Na2CO3 + 10H2O → Na2CO3 . 10H2O (Sodium carbonate)



When Na2CO3 10H2O is strongly heated then the following reaction takes place.



strong. heating. Na2CO3 10H2O    → Na2CO3 + 10H2O

(soda ash)

Uses: 

In the manufacture of glass, soap, paper and other sodium compounds such as borax, caustic soda etc.  for removing permanent hardness of water  In laundry as washing soda 22


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

As a cleansing agent for domestic purposes  As a laboratory reagent. Na2CO3 . 10H2O is an efflorescent salt i.e. at room temperature it gives out 9 molecules of its water of crystallization and dissolves in this water. This phenomenon is called efflorescence room.temp. Na2CO3 . 10H2O   → Na2CO3 . H2O + 9H2O

That is why washing soda is sold as soda ash in grocer shops.

Crystals of Salts are not dry: 

Blue copper sulphate crystals which seem to be dry contain water of crystallisation. When we heat the crystals, this water is removed and the salt turns white.  If you moisten the crystals again with water, you will find that the blue colour of the crystals reappears.  Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt. Five water molecules are present in one formula unit of copper sulphate. Chemical formula for hydrated copper sulphate is CuSO4 . 5H2O.  One other salt, which possesses water of crystallization is gypsum. It has two water molecules as water of crystallization. It has the formula CaSO4.2H2O.

Plaster of Paris:  Formula: CaSO4 ½H2O hemihydrated salt of calcium sulphate.

Preparation: 

It is prepared by controlled heating of gypsum at 373 K in a kiln. 373 K CaSO4 • 2H2O  → (CaSO4) • ½H2O + 1½H2O

Note: If heating is not controlled anhydrous calcium sulphate is formed. This is called burnt gypsum. Properties: 

Plaster of Paris is a white powder. When it is mixed with water, crystals of gypsum are produced again, but this time they are set to form a hard solid mass. CaSO4 ½H2O + 1½ H2O → CaSO4 2H2O Plaster of Paris

Gypsum



Half a water molecule is shown to be attached as water of crystallisation. It is written in this form because two formula units of CaSO4 share one molecule of water.  About 5000 years ago, Egyptians obtained a powder by heating gypsum (calcium sulphate) in open air fires.  This powder was used for cementing blocks of their monuments. The powder is called plaster of Paris because it is made by using gypsum, which was mainly found in Montmartre in Paris. 

APPENDIX: NCERT ACTIVITIES Activity 2.1: Aim: To show how the following solutions behave in the presence of different indicators Apparatus: HCl, H2SO4, HNO3, CH3COOH, NaOH, Ca(OH)2, KOH, Mg(OH)2, NH4OH, watch – glass, phenolphthalein, Methyl orange, red litmus, blue litmus.

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Procedure: Collect the following samples. Put a drop of each of the above solutions on a watch–glass and test with a drop of the following indicators as shown in the table. Observe the changes taking place in each of the solutions. Observation: Sample Red litmus Blue litmus Phenolphthalein Methyl orange solution solution solution solution solution HCl Red Red Colourless Reddish Orange H2SO4 Red Red Colourless Reddish Orange HNO3 Red Red Colourless Reddish Orange CH3COOH Red Red Colourless Reddish Orange NaOH Blue Blue Pink Yellow Ca(OH)2 Blue Blue Pink Yellow KOH Blue Blue Pink Yellow Mg(OH)2 Blue Blue Pink Yellow NH4OH Blue Blue Pink Yellow Conclusion: These indicators tell us whether a substance is acidic or basic by change in colour of the indicator solutions. Activity 2.2: Aim: Use of some olfactory indicators. Apparatus: finely chopped onions, plastic bag, some strips, of clean cloth, HCl, NaOH, dilute, vanilla, essence and clove oil, test tubes. Procedure: Take some finely chopped onions in a plastic bag put some strips of clean cloth in the bag. Tie up the bag tightly and leave overnight in the fridge. The cloth strips can now be used to test for acids and bases. Take two of these cloth strips and check their odour. Keep them on a clean surface and put a few drops of dilute HCl solution on one strip and a few drops of dilute NaOH solution on the other. Rinse both cloth strips with water and again check their odour. Note your observations. Now take some dilute vanilla essence and clove oil and note their odour. Take some dilute HCl solution in one test tube and dilute NaOH solution in another. Add a few drops of dilute vanilla essence to both test tubes and shake well. Check the odour once again and record changes in the odour, if any. Similarly, test the change in the odour of clove oil with dilute HCl and dilute NaOH solutions and record your observations. Observation: The cloth strips smell of onion even when a few drops of dilute HCl and dilute NaOH are put on them. When vanilla and clove essences are added to the test tubes containing dilute HCl and dilute NaOH, their smell is still felt. Conclusion: Vanilla, onion and clove, can be used as olfactory indicators. Activity 2.3: Aim: To show how acids react with metals. Apparatus: 5 ml of dilute sulphuric acid in a test tube a few pieces of zinc granules, soap solution, burning candle, HCl, HNO3, CH3COOH. Procedure: Take about 5 ml of dilute sulphuric acid in a test tube and add a few pieces of zinc granules to it. Pass the gas being evolved through the soap solution Take a burning candle near a gas filled bubble. Repeat this activity with some more acids like HCl, HNO3 and CH3COOH Observation: The zinc granules are dull and coated, and hydrogen gas is evolved. This gas burns with a blue flame and with a pop sound. When this activity is repeated with HCl and CH3COOH the same observation is observed. But with HNO3; H2 gas is not evolved. 24


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Conclusion: All highly reactive metals (eg. Na, Mg, Al) liberate hydrogen when they react with HCl, H2SO4, CH3COOH. Lower reactive metals do not liberate H2 with CH3COOH Delivery tube Stand Burning of hydrogen gas with a pop sound Test tube Dil. sulphuric acid

Candle Hydrogen gas bubbles

Zinc granules

Soap bubble filled with hydrogen

Soap solution Reaction of zinc granules with dilute sulphuric acid and testing hydrogen gas by burning

Activity 2.4: Aim: To show how metals react with bases Apparatus: a few pieces of granulated zinc metal in a test tube. Sodium hydroxide solution and burner, soap solution and a burning candle. Procedure: Place a few pieces of granulated zinc metal in a test tube. Add 2 ml of sodium hydroxide solution and warm the contents of the test tube. Pass the gas being evolved through the soap solution. Take a burning candle near a gas filled bubble. Observation: hydrogen gas is evolved which burns with a blue flame and a ‘pop’ sound. Conclusion: When a metal reacts with a base hydrogen is formed in the reaction. However, such reactions are not possible with all metals. Activity 2.5: Aim: Reaction of acids with metal carbonates and Thistle funnel Stand metal hydrogencarbonates Cork Delivery tube Apparatus: two test tubes, 0.5 g of sodium Test tube carbonate, 0.5 g of sodium hydrogencarbonate, lime water, 2 ml of dilute HCl Procedure: Take two test tubes, label them as A Carbon dioxide gas Dilute and B. Take about 0.5 g of sodium carbonate Test tube Calcium Hydrochloric (Na2CO3) in test tube A and about 0.5 g of sodium hydroxide acid Sodium solution hydrogencarbonate (NaHCO3) in test tube B. Add carbonate about 2ml of dilute HCl to both the test tubes. Pass the gas produced in each case through lime water (calcium hydroxide solution) as shown in fig. Observation: We observe that in both the cases carbon dioxide is liberated and on passing the carbon dioxide gas evolved: through lime water, .it turns milky. Conclusion: The following reactions take place. Test tube A: Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g) Test tube B: NaHCO3(s) + HCl(aq) → NaCl(aq) + H2O(l) + CO2(g) Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l) (Lime water)

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(White precipitate)


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Activity 2.6: Aim: To show how acids and bases react with each other (Neutralization). Apparatus: 2 ml of dilute NaOH solution, two drops of phenolphthalein, 2 ml of dilute HCl solution. Procedure: Take about 2 ml of dilute NaOH solution in a test tube and add two drops of phenolphthalein solution. Add 2 ml of dilute HCl solution to the above solution drop by drop. Now add a few drops of NaOH to the above mixture. Observation: The colour of the solution when phenolphthalein is added to dilute NaOH turns pink. When dilute. HCl is added to the above solution the colour of the solution turns colourless. This has happened because phenolphthalein is colourless in neutral medium. When we add a few drops of NaOH to the above mixture the pink colour of phenolphthalein reappears because the solution has become basic Conclusion: The reaction taking place is written as NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l) The reaction between an acid and a base to give a salt and water is known as a neutralization reaction. In general, a neutralization reaction can be written as Base + Acid → Salt + Water. Activity 2.7: Aim: Reaction of Metallic Oxides with acids. Apparatus: Small amount of copper oxide, beaker, dilute hydrochloric acid, Procedure: Take a small amount of copper oxide in a beaker and add dilute hydrochloric acid slowly while stirring. Observation: Copper oxide gets converted to copper chloride which is greenish blue in colour. Conclusion: The following reaction has taken place CuO + 2HCl → CuCl2 + H2O. The general reaction between a metal oxide and an acid can be written as, Metal oxide + Acid → Salt + water. This reaction proves that metallic oxides are basic in nature. Activity 2.8: Bulb 6 volt battery Aim: To show that acids and bases conduct electricity Switch Apparatus: glucose, alcohol, hydrochloric acid, sulphuric acid, NaOH, Ca(OH)2 few 100 ml beakers, 6 volt batteries, bulbs, switches, few nails and corks. Beaker Procedure: Take solutions of glucose, alcohol, hydrochloric acid, sulphuric acid, NaOH, Ca(OH)2 each, in a 100 ml beaker, Nail Dilute HCl Fix two nails on a cork, and place the cork in each beaker. solution Connect the nails to the two terminals of a 6 volt battery Rubber through a bulb and a switch, as shown in Fig. Switch on the cork current Observation: The bulb will start glowing in the case of acids and bases as they do not ionse when electricity is passed through them. Glucose and alcohol solutions do not conduct electricity. So the bulb will not glow in these solutions. Conclusion: Glowing of the bulb indicates that there is a flow of electric current through the solution. The electric current is carried through the solution by ions. Since the cation present in + + acids is H , this suggests that acids produce hydrogen ions, H (aq) in solution, which are responsible for their acidic properties which carry electricity with them. Using alkalis such as sodium hydroxide calcium hydroxide, etc we see that the bulb glows i.e. these solutions conduct – – electricity with the help of OH ions, these OH ions produced by bases are responsible for their basic properties

26


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Activity 2.9: Aim: To show that acids and bases produce ions in aqueous solutions Apparatus: 1g solid NaCl, clean and dry test tube, some concentrated sulphuric acid, with dry and wet blue litmus papers. Procedure: Take about 1g solid NaCl in a clean and dry test tube and set up the apparatus as shown in the Fig. Add some concentrated sulphuric acid to the test tube. Test the gas evolved successively with dry and wet blue litmus paper. Observation: A gas HCl is liberated and has no reaction on dry blue litmus paper but it turns wet blue litmus paper red + Conclusion: Hydrogen ions in HCl are produced in the presence of water. The separation of H + − ions from HCl molecules cannot occur in the absence of water. Eg. HCl + H2O → H3O + Cl H O

Similarly when a base is dissolved in water. Eg. NaOH(s) 2→ Na (aq) + OH (aq) – – They generate hydroxide (OH ) ions in water. These OH ions turn moist red litmus paper blue but they have no effect on dry blue litmus paper. Activity 2.10: Aim: To show that heat is evolved when acids or bases are added to water Apparatus: 10 ml water, beaker, few drops of concentrated H2SO4, few sodium hydroxide pellets Procedure: Take 10 ml water in a beaker. Add a few drops of concentrated H2SO4 to it and swirl the beaker slowly. Touch the base of the beaker Repeat the above activity with sodium hydroxide pellets and record your observations. Observation: The beaker becomes hot when diluting acids and bases. Conclusion: Heat is liberated when acids and bases are diluted. Activity 2.11: Aim: To test the pH values of certain given solutions. Apparatus: pH papers, solutions listed in table Procedure: dip the pH papers separately in each given solution. Observation: S. Colour of Approximate Solution No. pH paper pH value 1 Saliva (before meal) light green 8 2 Saliva (after meal) orangish red 5 3 Lemon juice orange 2 4 Colourless aerated drink orange 3 5 Carrot juice light yellow 4 6 Coffee orange 3 7 Tomato juice orange 3 8 Tap water orange 4 9 1 M NaOH dark blue 13 10 1 M HCl dark red 1 Conclusion: from the above observation we discern the pH value given solution.

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+

–

Nature of substances weekly basic weekly acidic weekly acidic acidic weekly acidic acidic acidic weekly acidic strongly basic strongly acidic and hence the nature of the


27

28

Activity 2.12: Aim: To test the ideal soil pH for the growth of plants. Apparatus: 2 g of soil, 5 ml water, universal indicator paper, filter paper and a test tube. Procedure: Put about 2 g of soil in a test tube and add 5 ml water to it. Shake the contents of the test tube. Filter the contents and collect the filtrate in a test tube. Check the pH of this filtrate with the help of universal indicator paper. It is found to be between 6.0 – 7.5. Observation: Plants grow healthily in a specific pH range i.e. between 6.0 – 7.5. Conclusion: Hence we have to prepare an ideal soil (pH between 6.0 – 7.5) for their healthy growth. Activity 2.13: Write the formulae of the salts given below: Potassium, sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate, sodium chloride, sodium nitrate, sodium carbonate and ammonium chloride. Identify the acids and bases from which the above salts may be obtained. H2SO4 + KOH Potassium sulphate K2SO4 Sodium sulphate: Na2SO4 H2SO4 + NaOH Calcium sulphate: CaSO4 H2SO4 + Ca(OH)2 SO4/H2 family Magnesium sulphate: MgSO4 H2SO4 + Mg(OH)2 Copper sulphate: CuSO4 H2SO4 + Cu(OH)2 Sodium chloride: NaCl HCl + NaOH Chloride family Sodium nitrate: NaNO3 HNO3 + NaOH Nitrate family Sodium carbonate: Na2CO3 H2CO3 + NaHCO3 Sodium/Carbonate family Ammonium chloride: NH4Cl HCl + NH4OH Ammonium/Chloride family Activity 2.14: Aim: To find pH of certain salt solutions. Apparatus: pH paper, sodium chloride, potassium nitrate, aluminium chloride, zinc sulphate, copper sulphate, sodium acetate, sodium carbonate and sodium hydrogencarbonate. Procedure: Salt pH Nature sodium chloride 7 neutral potassium nitrate 7 neutral aluminium chloride 7 neutral zinc sulphate 7 neutral copper sulphate 7 neutral sodium acetate 8 basic sodium carbonate 8 basic sodium hydrogencarbonate 8 basic Conclusion: from the above observation we discern the pH value and hence the nature of the given salt solution. Activity 2.15: Aim: To show that crystals of salts are not dry. They contain water of crystallization. Apparatus: few crystals, of copper sulphate, a dry boiling tube, burner. Procedure: Heat a few crystals of CuSO4 in a dry boiling tube. Add 2-3 drops of water on the sample of copper sulphate obtained after heating Observation: Coppersulphate crystals contain water of crystallization. When we heat the crystals, this water is removed and the salt turns white. If you moisten the crystals again with water, you will find that blue colour of the crystals reappears. Conclusion: Water of crystallization is the fixed number of water molecules present in one formula unit of a salt. It is responsible for the colour of the crystal. 28


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Activity 2.16: Aim: To show that alcohol and glucose contain hydrogen but are not acids. Apparatus: alcohol, glucose, HCl, HNO3, H2SO4 and H2CO3. Procedure: Prepare aqueous solutions of alcohol, glucose, HCl, HNO3, H2SO4 and H2CO3. Take a 100 ml capacity beaker and attach two carbon electrodes to a card–board. Connect the electrodes to a 6V battery, ammeter and a torch bulb as shown in the fig. Fill the beaker with aqueous solution of alcohol and then with glucose and see whether the bulb glows or not. Now fill the beaker with aqueous solution of hydrochloric acid and then with aqueous solutions of other acids separately and see whether the bulb glows or not. Observation: In case of aqueous solutions of acids bulb glows but in case of aqueous solutions of alcohol and glucose the bulb does not glow. Conclusion: Aqueous solution of an acid is ionic i.e. hydrogen present in acids changes to + + hydrogen ions (H ) in aqueous solutions of an acid. The H ions move to cathode and change to hydrogen gas taking one electron. + – H + H → H2 H + 1e → H + But alcohol and glucose do not ionise to release H ions so they do not conduct electricity. Hence alcohols and glucose are not acidic in nature. REVIEW QUESTIONS: CW Exercise: Very Short Answer: 1 Mark 1) Give one example in case of a reaction which takes place, at moderate rate. 2) Define i) strong electrolyte ii) acid iii) out of dilute H2SO4 and conc. CH3COOH which is a weak electrolyte? 3) Vinegar is dilute _______ acid. 4) What do you understand by the term strength of an acid? 5) Define i) strong acid ii) weak acid 6) What is the effect of an acid on slightly alkaline blue litmus solution? 7) What product is liberated at cathode when electric current is passed through an aqueous acid solution? 8) What is a base? 9) Amongst Fe (OH)2 and NaOH which is a base which is an alkali? 10) Give one example of a strong alkali and one example of a weak alkali. 11) What is the effect of an alkali on slightly acidic red litmus solution? 12) What is meant by pH of a solution? 13) Name the scientist who introduced pH scale? 14) What is pH scale? + 15) What is the conc. of H (aq) ions in distilled water? + 16) Two solutions P and Q have pH 2 and 12. Which solution has more concentration of H (aq) ions? 17) A solution has pH + 6. Is it acidic or basic? 18) Give the formula of bleaching powder. 19) Which compound is used for cooking purposes? Na2CO3 / NaHCO3 20) Give the formula of slaked lime. Volume


29

30

21) 22) 23) 24) 25) 26) 27)

Name a sodium compound used to soften hard water. What is the common name of CaOCl2? What is the role of NaHCO3 in baking powder? What happens when Na2CO3. 10H2O crystals are exposed to air? Name the constituents of baking powder. What happens when Bleaching powder is left exposed to air containing CO2 gas? State the chemical difference between Plaster of Paris and Gypsum. Describe their inter conversions. Short Answer: 2 Marks 28) State whether a solution is acidic, alkaline or neutral if its pH is i) 2 ii) 12 and iii) 7. 29) State the important properties of washing soda. 30) What is the common name of Na2CO3.10H2O? Name a metal carbonate, which is soluble in water. 31) Give two important uses of washing soda. 32) Give two important properties of baking soda. 33) A baker found that the cake prepared by him is hard and small in size. Which ingredient had he forgotten to add that would have made the cake fluffy? Give reasons. 34) What happens when bleaching powder is exposed to air? 35) Write the chemical equations for the reactions involved in the manufacture of bleaching powder? 36) Explain giving reasons, i) Tartaric acid is a component of baking powder used in making cakes ii) Gypsum CaSO4. 2H2O is used in the manufacture of cement. 37) Write fully balanced equations when: i) washing soda crystals are strongly heated ii) Baking soda crystals are strongly heated. 38) Is the solution of washing soda acidic or alkaline in nature? Give the chemical formula of washing soda. 39) What is gypsum? What happens when gypsum is heated to 373 K. Support your answer by a chemical equation? 40) What is the chemical name of washing soda? 41) State the chemical property in each case on which the following uses of baking soda are based i) as an antacid ii) as a constituent of baking powder. Short Answer: 3 Marks 42) A solution has a pH + 4. Is the solution acidic or basic? 43) What do you understand by the term, neutralization? Give two practical uses of neutralization. 44) pH of a solution changes from 5 to 4. What changes do you expect in H ion concentration. Long Answers: 3 Marks 45) Name the compound, which is used in hospitals for setting fractured bones. Write its chemical name and formula. How is it prepared? 46) Give important uses of Plaster of Paris. 47) What is meant by water of crystallization? Write the chemical formula of blue copper sulphate showing water of crystallization in it. How will you experimentally show the presence of water in the crystals of CuSO4? 48) What is acid rain? How could it affect the Taj Mahal in Agra? 49) Complete the equations given below. i) Ca(OH)2 + Cl2 → ______ + ______. 50) Describe with chemical equations, what happens when i) Dry Cl2 is passed over solid slaked lime ii) Na2CO3 crystals are kept in air. 30


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iii) Gypsum is heated at 120°C Long Answer: 5 Marks 51) What is the importance of pH value in i) medicine ii) cosmetics

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iii) agriculture

HW Exercise: Fill in the blanks: 1) When the pH of a solution is above 7 the solution is _______ + – 2) _______ is a chemical reaction in which H3O ions of an acid and OH ions of a base combine to form unionised water. 3) During the process of _______ of ionic compounds the water mainly sets free the ions, which are already present in the solid compound 4) The calcium sulphate hemihydrate is commonly known as _______. 5) Concentrated NaCl is called _______. 6) _______ sodium carbonate is commonly called soda ash 7) When water is added to Plaster of Paris to harden it forms crystals of _______. State whether the statements given below are true or false: 8) The pH of all alkali solutions is less than 7 2+ – 9) The process of breaking lead bromide into Pb . Br ions is called ionisation. 10) An acid is a substance which in a solution furnishes positively charged ions. 11) The solution of baking soda in water is alkaline in nature. 12) Baking soda is used in the manufacture of aerated waters. 13) CO2 reacts with bleaching powder to form CaSO4 and Cl2 gas. Multiple Choice Questions: (Tick the correct answer) 14) When CH3COOH is dissolved in water it furnishes + – – a) H (g) and CH3COO (l) ions b) H2(g) and CH3COO (l) ions + – – c) H (aq) and CH3COO (aq) ions d) H2(aq) + CH3COO (aq) ions 15) The pH of a neutral solution at 298K is a) 2.0 b) 12 c) 0 d) 7 16) The correct formula for Plaster of Paris is a) CaSO4 . ½ H2O b) 2CaSO4 . H2O c) (CaSO4)2 . H2O d) CaSO4 . 2H2O 17) Which aqueous solution of the following salts turns blue litmus red? b) NaHCO3 c) Na2CO3 . 10H2O d) none of these a) Na2CO3 18) Which of the following reactions represent reduction of CO2 heat a) CaCO3  → CaO + CO2

heat b) C + O2  → CO2

d) CaOCl2 + CO2 → CaCO3 + Cl2 c) CO2 + C → 2CO 19) Which of the following pairs, are both chemically the same a) Limestone and Marble b) Slaked lime and Quicklime c)Gypsum and Plater of Paris d) Alumina and Gypsum 20) The chemical formula of washing soda is b) Na2CO3 . 9H2O c) Na2CO3 d) Na2CO3 . 10H2O a) Na2CO3 . H2O Volume


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Very Short Answers: 1 Mark 21) Give differences between acids and bases. (4 pts.) 22) Mention the pH of a neutral solution? 23) State the pH of a strong acid? 24) What is the pH of a weak base? 25) State the pH of acids? 26) Mention the pH of bases? 27) Acid turns ______ litmus ______. 28) A solution has pH = 3, is it an acid or base? 29) What is the chemical name of baking soda? 30) A white chemical compound becomes hard on mixing proper quantity of water. It is also used in surgery to maintain joints in a fixed position. Name the chemical compound. 31) What is soda ash? 32) Name the gas evolved when washing soda is treated with acetic acid. 33) What is the chemical formula of baking soda? 34) Give three uses of baking soda, other than in the preparation of baking powder 35) What happens when Cl2 is added to milk of lime? 36) Name the compound used for reducing acidity of soil? 37) Name the raw materials required in the manufacture of bleaching powder 38) Give three uses of bleaching powder other than bleaching of cotton fabrics. 39) Name the civilization credited for the discovery of Plaster of Paris. 40) Name the raw materials from which Plaster of Paris is prepared 41) Give one use of Plaster of Paris in the construction of houses. 42) Write the chemical equation to show effect of heating gypsum at 100°C. 43) What are washing soda and baking soda chemically? 44) Why does bleaching powder decompose on exposure to air? Short Answers: 2 Marks 45) Complete the reactions: i) Na2S + CaCO3 → ______ + CaS, ii) Na2CO3+H2O→ ______. 46) Name the substance obtained by the action of chlorine on dry slaked lime. Write a chemical equation for the reaction. 47) What happens when crystals of washing soda are exposed to air? Support your answer by relevant chemical equations. 48) How can you obtain soda ash from washing soda crystals? Support your answer by a chemical equation. 49) Starting from Sodium hydrogen carbonate how can you obtain anhydrous Na2CO3? Support you answer by a chemical equation. 50) How will you convert Na2CO3 to baking soda? Support your answer by a chemical equation. 51) Why is washing soda marketed as soda ash? 52) Why is aqueous solution of Na2CO3 alkaline in nature? 53) Complete the following equations. Na2 CO3 + ______ → Na2SO4 + ______ + ______ 54) What will you observe when water is slowly poured over quicklime? 55) What determines the quality of bleaching powder 56) Why is bleaching powder kept in air tight containers? 32


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57) Bleaching powder is soluble in water. However, when dissolved in water it leaves behind some white residue explain. 58) i) CaOCl2 + HCl ______ ______ + ______ + ______ ii) Ca(OH)2 + Cl2 ______ ______ ______ 59) What is calcium sulphate hemihydrate commonly known to us as? List its two uses. 60) A compound which is prepared from gypsum has a property of hardening when mixed with a proper quantity of water. Identify the compound; write the chemical equation, for its preparation. Mention one important use of the compound. 61) A compound of calcium having an odour of chlorine is used to remove yellowness of white clothes in laundries. Name the compound. Write chemical equations involved in its preparation. 62) Ca(OH)2 is used for white washing, why? 63) Bleaching Powder always smells of chlorine, why? NCERT EXERCISE: 1) You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube? 2) Why should curd and sour substances not be kept in brass and copper vessels? 3) Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example, how will you test for the presence of this gas? 4) Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride. 5) Why do HCl, HNO3 etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character? 6) Why does an aqueous solution of inorganic acid conduct electricity? 7) Why does dry HCl gas not change the colour of the dry litmus paper? 8) While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid? + 9) How is the concentration of hydronium ions (H3O ) affected when a solution of an acid is diluted? – 10) How is the concentration of hydroxide ions (OH ) affected when excess base is dissolved in a solution of sodium hydroxide? 11) You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic? + 12) What effect does the concentration of H (aq) ions have on the nature of the solution? + 13) Do basic solutions also have H (aq) ions? If yes, then why are these basic? 14) Under what soil conditions do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)? 15) What is the common name of the compound CaOCl2? 16) Name the substance which on treatment with chlorine yields bleaching powder. 17) Name the sodium compound which is used for softening hard water. 18) What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved. 19) Write an equation to show the reaction between Plaster of Paris and water. 20) A solution turns red litmus blue, its pH is likely to be a) 1 b) 4 c) 5 d) 10 21) A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains a) NaCl b) HCl c) LiCl d) KCl Volume


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22) 10 ml of a solution of NaOH is found to be completely neutralised by 8 ml of a given solution of HCl. If we take 20 ml of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralise it will be a) 4 ml b) 8 ml c) 12 ml d) 16 ml 23) Which one of the following types of medicines is used for treating indigestion? a) Antibiotic b) Analgesic c) Antacid d) Antiseptic 24) Write balanced equations for the reactions taking place when a) dilute sulphuric acid reacts with zinc granules b) dilute hydrochloric acid reacts with magnesium ribbon c) dilute sulphuric acid reacts with aluminium powder d) dilute hydrochloric acid reacts with iron filings 25) Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an activity to prove it. 26) Why does distilled water not conduct electricity, whereas rain water does? 27) Why do acids not show acidic behaviour in the absence of water? 28) Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is a) neutral? b) strongly alkaline? c) strongly acidic? d) weakly acidic? e) weakly alkaline? Arrange the pH in decreasing order of hydrogen-ion concentration. 29) Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and why? 30) Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer. 31) A milkman adds a very small amount of baking soda to fresh milk. a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline? b) Why does this milk take a long time to set as curd? 32) Plaster of Paris should be stored in a moisture-proof container. Explain why? 33) What is a neutralisation reaction? Give two examples. 34) Give two important uses of washing soda and baking soda. MULTIPLE CHOICE QUESTIONS: PRACTICAL THEORY 1) Reaction between HCl and NaOH is called a) Displacement b) Combination c) Double displacement d) Neutralization 2) What is the taste of bases? a) The taste of bases is bitter b) The taste of bases is sour c) They have no taste at all d) They taste sweet 3) The gas produced on adding sodium carbonate to acids is: a) Hydrogen b) Oxygen c) Carbon monoxide d) Carbon dioxide 4) What is the effect of sodium hydroxide on litmus? a) Sodium hydroxide changes red litmus to blue b) Sodium hydroxide allows red litmus to stay red c) Sodium hydroxide changes blue litmus to red d) Sodium hydroxide has no effect on litmus 34


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5) Which one of the following solutions turns red litmus blue? a) Water b) Milk c) Ethanoic acid d) Sodium hydroxide 6) Bottle A contains dilute HCl and bottle B contains sodium bicarbonate solution. When pH paper is dipped in each bottle, the colour seen in A and B respectively is a) Blue, orange b) Green, blue c) Orange, blue d) Orange, green 7) On adding sodium carbonate to sodium hydroxide: a) Hydrogen gas is produced b) Carbondioxide gas is formed c) Carbon monoxide gas is produced d) No reaction occurs. 8) Which of the following is most acidic? a) dil. Hydrochloric acid b) dil. ethanoic acid c) oxalic acid d) methanoic acid 9) Which of the following is the correct chemical formula of sodium zincate? a) NaZnO2 b) Na2ZnO2 c) Na2Zn2O2 d) Na2ZnO4 10) NaOH turns blue litmus: a) Blue b) Green c) Colourless d) Red 11) HCl turns blue litmus: a) Blue b) Green c) Colourless d) Red 12) Basic nature of sodium hydroxide is due to the presence of: a) Hydroxide ion b) Sodium ion c) Hydrogen ion d) None of these 13) In the reaction given below which element is more reactive? Zn + CuSO4 → ZnSO4 + Cu a) Zinc b) Sulphur c) Copper d) Oxygen 14) Acetic acid turns blue litmus red. What happens when sodium hydroxide is added to it? a) The red litmus becomes blue b) The red litmus remains red c) The red litmus becomes colourless d) None of these 15) Acidic nature of hydrochloric acid is due to the presence of: a) Hydroxide ion b) Chloride ion c) Hydrogen ion d) None of these 16) HCl turns red litmus: a) Blue b) Green c) Colourless d) Red 17) Acetic acid turns blue litmus red. What happens when a few drops of dil. HCl are added to it? a) The red litmus becomes blue b) The red litmus remains red c) The red litmus becomes colourless d) None of these 18) On adding a pinch of sodium hydrogen carbonate to acetic acid, the gas produced is: a) Oxygen b) Carbondioxide c) Hydrogen d) Methane 19) What is observed when acetic acid and sodium bicarbonate are mixed? a) A colourless gas is liberated b) The colourless gas turns lime water milky c) The colourless gas turns blue litmus solution red d) All the above 20) On adding sodium carbonate to acetic acid, you immediately: a) Observe a strong effervescence b) Hear a hissing sound c) Get a pungent smell d) Notice formation of bubbles 21) The colour of acidified potassium dichromate solution is: a) Red b) Green c) Orange d) Yellow

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22) Four students studied reactions of zinc and sodium carbonate with dilute hydrochloric acid and dilute sodium hydroxide solutions and presented their results as follows. The ‘’ represents evolution of gas, where as ‘’ represents absence of any reaction Zn Na2CO3 Zn Na2CO3 Zn Na2CO3 Zn Na2CO3      A HCl    B C D         NaOH The right set of observations is that of student a) A b) B c) C d) D 23) To test the presence of an acid with a strip of red litmus paper you would a) Dip the strip in the acid as it is in the sample and see the colour change b) Moisten the paper with water and dip in the given sample c) First dip strip in the common salt solution and then use it to test the sample d) First dip strip in alkaline solution and then use it to test the sample 24) Which of the following salts turn blue litmus red when they are in their aqueous solutions? a) Na2CO3 b) NaHCO3 c) Ca(OH)2 d) None of these 25) When a few drops of a sample are added to universal indicator, then dark red colour is observed. The sample is a) HCl b) NaOH c) NaH CO3 d) H2O 26) When a few drops of a sample are added to universal indicator then red colour is observed. The pH of the sample is a) 0 to 3 b) 4 to 6 c) 6 to 8 d) 9 to 12 27) Na2CO3 is basic in nature because a) It turns red litmus blue b) It turns blue litmus blue c) It is bitter to taste d) All of the above 28) Four experimental setups are shown below

dilute HCl zinc

29) 30) 31)

32)

33) 36

dilute NaOH zinc

dilute HCl Na2CO3

dilute NaOH Na2CO3

The set ups that would result in rapid evolution of gas would be a) I and III b) II and IV c) I and II d) III and IV Bases are a) bitter to taste b) soapy to touch c) turns red litmus blue d) all of the above Acids are a) sour to taste b) bitter to taste c) soapy to touch d) none of the above An alkali is a) water insoluble base b) water soluble base c) partially soluble in water d) none of the above Bases are substances that release + – a) H ions when dissolved in water b) OH ions when dissolved in water c) Release gases when reacting with acids d) none of these When Na2CO3 is added to H2SO4 then a) H2 gas is liberated b) CO2 is liberated c) SO2gas is liberated d) none of the above Universal Tutorials – X CBSE (2012–13) – Chemistry

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34) The most appropriate method for testing the odour of a given liquid is:

I)

II)

III)

IV)

a) I b) II c) III d) IV 35) Acids release – + a) OH ions when dissolved in water b) H ions when dissolved in water c) react with bases to water and H2 gas d) none of these 36) When HCl and NaOH are reacted together a) neutralization takes place b) salt and water a formed c) No gas is evolved d) All of the above 37) When metal reacts with HCl and H2SO4 a) Cl2 gas is liberated b) H2 gas is liberated c) NO2 gas is liberated d) All of the above 38) CO2 can be tested by a) passing it through water and testing it with litmus solution b) passing it through lime water c) smelling it d) none of the above 39) CO2 turns a) red litmus solution blue b) blue litmus solution red c) indicator solution green d) none of these 40) The reaction between HCl and solid Na2CO3 is b) HCl + Na2CO3 → NaCl + CO2 + H2O a) 2HCl + Na2CO3 → 2NaCl + CO2 + H2O c) 2HCl + Na2CO3 → 2NaHCO3 + Cl2 d) none of the above 41) The test for hydrogen is a) A lighted splinter is brought near the gas and it burns with a blue flame and a pop sound is heard b) The gas is passed through water and tested with litmus solution c) The gas is made to react with a base to get salt and water 42) A solution turns red litmus blue its pH is likely to be a) 1 b) 4 c) 5 d) 10 43) Which of the following gas turns lime water milky? a) hydrogen b) oxygen c) carbon monoxide d) carbon dioxide 44) NaOH turns red litmus: a) blue b) green c) colourless d) red 45) CO2 gas turns moist blue litmus paper: a) white b) blue c) red d) colourless 46) A gas producing pop sound and burning with a blue flame is: a) nitrogen b) hydrogen c) oxygen d) carbon dioxide 47) Gas produced on adding NaOH to Zn metal is: a) hydrogen b) oxygen c) hydrogen and oxygen d) none of these 48) When a few drops of a sample are added to universal indicator then red colour is observed. The pH of the sample is a) 0 to 3 b) 4 to 6 c) 6 to 8 d) 9 to 12 Volume


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49) The zinc metal used in the laboratory for doing experiments is available in the form of: a) filings b) strips c) granules d) pellets 50) Zinc oxide is amphoteric because: a) it reacts only with NaOH b) it reacts only with HCl c) it reacts both with NaOH and HCl d) It does not react with NaOH and HCl 51) Lime water becomes milky on passing CO2 through it due to the formation of: a) Ca(OH)2 b) CaO c) CaCO3 d) none of these 52) What is the concentration of hydrogen ions in pure water? –7 –6 –4 –8 a) 10 mol/litre b) 10 mol/litre c) 10 mol/litre d) 10 mol/litre 53) The correct decreasing order of pH value of the following solutions is: a) water > lemon juice > sodium bicarbonate b) sodium bicarbonate > water > lemon juice c) lemon juice > water > sodium bicarbonate d) water > sodium bicarbonate > lemon juice 54) Which one is the correct method to find the pH of a solution?

a) I b) II c) III d) IV 55) What is the pH value of a solution of hydrochloric acid? a) pH less than 7 b) pH greater than 7 c) pH equal to 7 d) none of these 56) Four students I, II, III and IV of class X measured the pH value of each one of the given samples of distilled water, 0.1 M solution of ethanoic acid, 0.1 M solution of hydrochloric acid and 0.1 M solution of sodium hydroxide using pH papers at 298 K. Tell which one of the following represents a correct measurement? Student Water CH3COOH HCl NaOH I 7 1 1 1 II 7 3 1 1 II 7 1 1 13 IV 7 3 1 13 a) I b) II c) III d) IV 57) Sometimes chlorine gas is passed through water for its purification. The pH value of this water sample will be: a) Equal to 7 b) Less than 7 c) More than 7 d) Nearly 8 58) To find pH a) The pH paper is first dipped in Universal indicator. Then on drying; a drop of the solution is placed on a strip of the pH paper. The colour developed on the pH paper is compared with the pH colour strip on the chart and the corresponding pH value given on the chart is noted. b) The pH paper is first dipped in litmus indicator. Then on drying a drop of the solution is placed on the strip of the pH paper. The colour developed on the pH paper is compared with the colour of the strip on the chart and the corresponding pH value given on the chart is noted. c) A drop of the solution is placed on the strip of the pH paper. The colour developed on the pH paper is compared with the colour of the strip on the chart and the corresponding pH value given on the chart is noted. d) None of these 59) What is the pH of pure water? a) 7 b) 4 c) 6 d) 8 38


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60) The pH of NaOH is: a) Less than seven b) More than seven c) Seven d) Zero 61) Distilled water is a) acidic b) alkaline c) neutral d) None of these 62) We cannot find pH, using pH paper, of: a) Lemon juice b) Blood c) Washing soda d) Urine 63) pH of a solution is defined as the negative logarithm of a) Hydroxide ion concentration b) Oxide ion concentration c) Hydronium ion concentration d) None of these. 64) What is the pH value of a solution of sodium carbonate? a) Less than 7 b) seven c) More than 7 d) None of these 65) A student tested the pH of distilled water and found that the colour of the universal indicator paper changed to green. He checked the pH again after dissolving a pinch of common salt in it. The colour of the universal indicator paper this time was: a) Green b) Yellow c) Red d) Blue 66) The pH of lime juice is: a) > 7 b) < 7 c) 7 d) 0 67) Bottle A contains oxalic acid and bottle B contains sodium carbonate solution. When pH paper is dipped in each of the solutions, the colour seen in A and B respectively is: a) Orange, blue b) Blue, orange c) Green, blue d) Orange, green 68) A student observed that the colour of universal indicator paper changes to green when she/ he dipped it in water. She/ he added a few drops of concentrated hydrochloric acid to the water. The colour of universal indicator paper would turn to: a) Light red b) Apple green c) Dark blue d) Lemon yellow. 69) Which of the following has greatest pH: a) dil. sodium hydroxide solution b) dil. Sodium bicarbonate solution c) dil sodium carbonate d) dil ammonium chloride 70) A student was given three samples containing ethanoic acid, sodium bicarbonate solution and water in test tubes I, II and III respectively. On dipping a pH paper in them, he observed that the colour turned orange in I, blue in II and green in III. If arranged in increasing order of their pH, the sequence of these bottles would be: a) I, III, II b) I, II, III c) III, I, II d) II, III, I 71) The pH of HCl is: a) < 7 b) > 7 c) = 7 d) none of these 72) 7 is the pH of c) Pure water d) Salty water a) NaOH b) NaHCO3 73) What is the correct increasing order of the pH value of the following solutions? a) dil. sodium hydroxide solution, dil. hydrochloric acid, water b) dil. hydrochloric acid, dil. Sodium hydroxide solution, water c) water, dil. hydrochloric acid, dil. sodium hydroxide solution d) dil. hydrochloric acid, water, dil. sodium hydroxide solution 74) Solution having pH 11 is a) Basic b) Acidic c) Neutral d) None of these 75) Solution having pH less than 7 are a) Basic b) Acidic c) Neutral d) None of these 76) pH of the solution on adding acid to water: a) Decreases b) Increases c) Remains the same d) Can’t say 77) Universal indicator is a: a) Solution of phenolphthalein in alcohol b) Solution of phenolphthalein in water c) Mixture of many indicators d) Mixture of litmus solutions Volume


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78) Solution having pH 4 is a) Acidic b) Basic c) Neutral d) None of these 79) Which of the following is most suitable for finding the value of pH? a) pH paper b) Universal indicator c) pH meter d) None of these 80) Solutions having pH more than 7 are a) Acidic b) Basic c) Neutral d) None of these 81) The unit of hydrogen ion concentration in solution is: a) mol/litre b) mol litre c) litre/mol d) mol 82) The pH of orange juice is: a) > 7 b) < 7 c) 7 d) 0 83) pH of the solution on adding alkali to water: a) Decreases b) Increases c) Remains the same d) Can’t say 84) The two colours seen at the extreme ends of the pH chart are a) Red and blue b) Red and green c) Green and blue d) Orange and green 85) A student took the following samples to find out their pH using pH paper. The teacher remarked that one of the samples taken was not proper. The teacher was referring to a) Dilute hydrochloric acid b) Lemon juice c) toothpaste d) Soap solution 86) The pH of distilled water is ____ a) 0 b) 7 c) 11 d) 14 87) Indicators are solutions that a) Change the pH of the solutions when added to them b) Show the acidity or alkalinity of the solutions when added to them. c) Are strong organic compounds that change the colour of the solutions when added to them d) None of the above. 88) pH of milk is a) 6.6 b) 11.2 c) 7 d) 0 89) pH paper is used to find pH of a solution by a) dipping the pH paper in the solution directly b) By dipping it in water first and then dipping it in the said solution c) By dipping it in indicator and then dipping it in the given solution d) none of these 90) pH of a solution when [H+] = 10–6 is a) 6 b) 1/6 c) –6 d) none of these 91) Between HCl and ethanoic acid HCl is a) more acidic than ethanoic acid b) less acidic than ethanoic acid c) their acidities are the same d) none of these 92) Between NaOH and NaHCO3 the pH of NaOH is a) more than that of NaHCO3 b) less than that of NaHCO3 c) same as that of NaHCO3 d) none of the above 93) The new pH on adding water to HCl solution having pH 4 is a) less than 4 b) more than 4 c) 4 d) can’t say 94) The new pH on adding water to NaOH solution having pH 10 is a) less than 10 b) more than 10 c) 10 d) can’t say 95) The solution turning blue litmus red is a) NaOH b) dil HCl c) milk d) NaHCO3 40


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96) Bottle A contains acetic acid and bottle B contains Na2CO3 solution. When pH paper is dipped in each of the solutions the colour seen in A and B respectively will be a) orange blue b) blue orange c) green blue d) orange green 97) The pH of distilled water on adding lemon juice is a) > 7 b) < 7 c) 7 d) none of these 98) If pH of a solution is 12 then the solution may be a) H2O b) HCl c) NaOH d) HNO3 99) When a few drops of a sample are added to universal indicator green colour is observed. The sample is a) 9 to 11 b) 2 to 4 c) 12 to 14 d) 6 to 8 100) When a few drops of a sample are added to universal indicator, then dark red colour is observed. The sample is a) HCl b) NaOH c) NaH CO3 d) H2O ANSWERS: Review Questions: CW + 3) acetic acid 16) The solution with pH = 2 has more conc. of H (aq) ions 18) CaOCl2 19) NaHCO3 20) Ca(OH)2 21) Washing soda Review Questions: HW 1) alkaline 2) neutralization 3) dissociation 4) Plaster of Paris 5) Brine 6) Anhydrous 7) Gypsum 8) False 9) True 10) True 11) True 12) False 13) False 14) c 15) d 16) a 17) d 18) c 19) a 20) d 62) The calcium hydroxide solution applied to the walls reacts slowly with the CO2 from air to form CaCO3 that gives a bright appearance to the walls 63) Because when exposed to air it decomposes to give Cl2 gas CaOCl2 → CaO + Cl2 NCERT Exercise: 1) i) In distilled water, red litmus remains red ii) In basic solution, Red becomes blue 2) i) They being acidic in nature react with metal, brass and copper liberating hydrogen. ii) They react with the surface of brass and copper to form salts of copper which are toxic and unfit for consumption. 3) Hydrogen, Zn + 2HCl → ZnCl2 + H2. The gas is tested by burning it. A blue flame is seen and a popping sound is heard. 4) CaCO3 + 2HCl → CaCl2 + CO2 + H2O + 5) Because HCl and HNO3 ionize in water liberating H ions. Thus showing acidic characteristics, + but alcohol and glucose do not ionize in water and do not liberate H ions and thus do not show − acidic characteristics. HNO3 + H2O → H3O + NO3 +

6) Because inorganic acidic solutions ionize to liberate cations (H ) and anions which conduct electricity. + + 7) Dry HCl does not ionize liberating H ions. So, H ions are not there to change the colour of the + dry litmus paper. H ions are set free in the presence of water only. 9) Decreases the concentration per unit volume. – 10) OH ions increase per unit volume. If in case of weak base and strong base, weak base ionizes, – common ion OH remains constant. 11) A has more H(+aq) ion conc., A – acidic; B – Basic 12) It makes it acidic

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13) Basic solutions have less H(+aq) ions than OH ions, these OH ions are responsible for the basic –

–

nature of alkalies 14) If its pH is less than 6 to bring the pH between 6 − 7.5 which is ideal for agriculture. 15) Bleaching Powder 16) Ca(OH)2 17) Na2CO3 ∆ Na2CO3 + H2O + CO2 19) CaSO4 . ½H2O + 1½H2O → CaSO4 . 2H2O 18) 2NaHCO3 → 20) d 21) b 22) d 23) c b) Mg + 2HCl → MgCl2 + H2↑ 24) a) Zn + H2SO4 + ZnSO4 + H2↑ d) Fe + 2HCl → FeCl2 + H2 c) 2Al + 3H2SO4 → Al2(SO4)3 + 3H2 26) Pure water does not ionize so it is a bad conductor of electricity. Rain water is acidic in nature it ionizes and increases the hydrogen ion concentration. Hence it conducts electricity. 27) Acids ionize only in the presence of water. 28) (a) D (b) C (c) B (d) A (e) E; C E D A B 29) In test tube A HCl ionizes readily releasing hydrogen gas, while acetic acid does not ionize easily and so hydrogen gas is not easily released. So vigorous fizzing is not seen here. 30) pH value will decrease. Curd is acidic in nature. Increase in hydrogen ion conc. decreases pH value. 31) (a) To prevent it from curdling i.e. becoming acidic and splitting. (b) Its pH is alkaline 32) It absorbs moisture, hardens and forms gypsum. CaSO4 . ½ H2O + 1½H2O → CaSO4 . 2H2O

Note: Not all questions have been solved from the exercises behind the chapter. Students are expected to answer these questions on their own on completion of the chapter.

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Chapter 03: Metals and Non–Metals

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Chapter 03: Metals and Non–Metals Chapter Map: Metals

Non–Metals

→ Properties (Physical and Chemical) Properties (Physical and Chemical)

→ Activity Series → Electronic Configuration of some elements → Properties of Ionic Compounds → Occurrence (Minerals and Ores) → Metallurgy / Extraction → Enrichment of Ore → Conversion of Ore to Metal Oxide

→ Heating → Extracting Metals Low in the Activity Series → Calcination → Extracting Metals in the Middle of the Activity Series → Roasting → Extracting Metals towards the Top of the Activity Series → Reduction → Electrolytic Reduction → Refining → Electrolytic Refining → Alloy → Steel → Alloy of gold → Corrosion → Prevention of corrosion

Introduction:  Elements can be classified as metals or non–metals on the basis of their physical and chemical properties.  Metals and non–metals form a very useful part of our daily life. We use metals and non–metals in every walk of life, home and Industry. Metals are used to manufacture utensils, containers, furniture, air–conditioners, computers, modes of transport, currency etc.  Non–metals are used to manufacture containers, furniture, currency, food stuffs, manufacture of compounds, explosives, combustion, fungicides etc.  There are more than 114 different chemical elements known and these elements possess a set of characteristic properties.  They are categorised into various groups considering their common features.  Thus we have metals, non–metals and metalloids.

Elements: 

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The simplest form of matter, which cannot be split into simpler substances by any chemical or physical method is called an element. Universal Tutorials – X CBSE (2012–13) – Chemistry

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Elements

Metals

Metalloids

Non – Metals

Rare gases

Metals:  A metal is an element, which forms positive ions by loss of electrons.  Large number of metals is present on the left-hand side and at the centre of the periodic table.  Non–metals are present on the right hand side of the periodic table.  (Except H which is on the left-hand side)  There are around 80 metals known to us.  All the metals are solids except for Hg, Ga (melts on palm of hand).  Titanium, Chromium and Zirconium are called strategic metals as they are essential for the country’s economy and defence.

Non–metals:  There are around 22 non metals known, out of these 11 are gases, 1 is a liquid (Bromine) and the remaining 10 are solids

Metalloids  They are elements that show properties of both metals and non-metals. Eg: Si, Ge, As, Sb & Te.

Comparative Properties – Metals and Non Metals:  Metals and non–metals differ in physical and chemical properties.

Physical Properties: Comparative table for physical properties of Metals and Non–Metals: Property

44

Metals

Non-metals

Malleability

Malleable (They can be hammered into very thin sheets called foils) Gold and Silver are most malleable.

Not malleable

Ductility

Ductile (They can be drawn into wires)

Not ductile

Lustre (Shine)

Lustrous

Not lustrous (except diamond, graphite and iodine)

[Heat (Thermal) and Electricity]

Good conductors of heat and electricity (They offer little resistance to the flow of current, as they have free electrons in them). Lead and Mercury are poor conductors. Silver and copper are the best conductors of electricity

Poor conductors of heat and electricity (except graphite)

State

Solids (except Hg, Ga)

Maybe solids, liquids or gases


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Property

45

Metals

Non-metals

Melting Point/ Boiling Point

High M.P. (except Ga, Cs) and B.P. (except Na, K and Hg)

Low M.P. and B.P. (except diamond and graphite)

Hardness

Hard (except Na, Li and K)

Soft (except diamond)

Density

High densities (except Na, K, Li)

Low densities

Sound

Sonorous (When metals are hit with an object they produce sound)

Non – sonorous

Tensile Strength

High tensile strength

Low tensile strength



 

 

All metals except mercury and Galium exist as solids at room temperature. Metals have high melting points but gallium and caesium have very low melting points. These two metals will melt if you keep them on the palm of your hand. Iodine is a non-metal but it is lustrous. Carbon is a non-metal that can exist in different forms. Each form is called an allotrope. Diamond, an allotrope of carbon, is the hardest natural substance known and has a very high melting and boiling point. Graphite, another allotrope of carbon, is a conductor of electricity. Alkali metals (lithium, sodium, potassium) are so soft that they can be cut with a knife. They have low densities and low melting points. Elements can be more clearly classified as metals and non-metals on the basis of their chemical properties.

Chemical Properties: Comparative table for chemical properties of Metals and Non-Metals: Metals Electropositive (They have a strong tendency to lose electrons from the outermost shell of their atoms and form positive ions (Cations)) Displace hydrogen from dilute mineral acids

Non Metals Electronegative (They have a strong tendency to accept electrons and form negative ions (Anions))

Form basic oxides / amphoteric oxides

Do not displace hydrogen from dilute mineral acids Form acidic oxides / neutral oxides

Form ionic chlorides, which conduct electric current Are reducing agents

Form covalent chlorides which do not conduct electricity Are oxidising agents (except graphite and coke)

Reactions of Metals: 1) With Oxygen: when burnt in air: 

Metals combine with oxygen to form metal oxides.  Metal (M) + Oxygen (O) → Metal Oxide (M2Ox : x = valency of metal) 4Al + 3O2 → 2Al2O3 Eg. 2Cu + O2 → 2CuO’ 

Atoms of metals lose electrons → + – Eg. Na → Na + e

positive metal ions

(2, 8, 1) (2, 8)

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46      

All metals do not react with oxygen at the same rate. Different metals show different reactivities towards oxygen. Metals such as potassium and sodium react so vigorously that they catch fire if kept in the open. At ordinary temperature, the surfaces of metals such as magnesium, aluminium, zinc, lead etc. are covered with a thin layer of oxide. Iron does not burn on heating but iron filings burn vigorously when sprinkled in the flame of the burner. Copper does not burn, but the hot metal is coated with a black coloured layer of copper(II) oxide. Silver and gold do not react with oxygen even at high temperatures.  Generally metal oxides are basic in nature. Some metal oxides dissolve in water to form alkalis e.g. Na2O(s) + H2O(l) → 2NaOH(aq)  But certain metal oxides are amphoteric in nature i.e. they show both acidic as well as basic natures. E.g. aluminium oxide, zinc oxide. 

Al2O3 + 2NaOH(aq) → 2NaAlO2(aq) + H2O (Acidic nature of Al2O3) Sodium aluminate

Al2O3 + 6HCl(aq) → 2AlCl3(aq) + 3H2O (Basic nature of Al2O3) Example (Magnesium forming magnesium oxide):

Mg → Mg2 + − O + 2e → O2 −

+

2e −

Mg + O → MgO Metal

(oxidation) (reduction)

Reaction Condition

Reaction

Na

Kept open in air at room temperature

Reacts to catch fire

Mg

Heated to ignition temperature

Burns producing intense heat and light

Cu

Heated for a long period

Reacts slowly

2) With Water: Metal + water → Metal oxide + H2  Metal oxide + water → Metal Hydroxide + H2.  In general metals react with water to form a metal oxide or hydroxide and hydrogen gas. But all metals do not react in the same way with water. 



46

Metals like K and Na react vigorously with cold water to form hydrogen gas. 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g) + heat energy Universal Tutorials – X CBSE (2012–13) – Chemistry

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2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) + heat energy The reaction of calcium with water is less violent. The heat evolved is not sufficient for the hydrogen to catch fire. Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g) Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal. In case of potassium, the reaction is so violent that the evolved hydrogen immediately catches fire. Mg does not react with cold water but only with hot water to form Magnesium Hydroxide and Hydrogen. Al, Zn, and Fe react only with steam to form metal oxide and hydrogen 2Al(s) + 3H2O(g) → Al2O3(s) + 3H2(g) 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g) Metal oxides are basic in nature. They react or dissolve in water to form an alkali



Na2O + H2O → 2NaOH K2O(s) + H2O(l) → 2KOH(aq) Metals such as lead, copper, silver and gold do not react with water at all.



   

3) With dilute acid:  

Metal + dil. Acid → Salt + Hydrogen Metals react with dilute acid, like dilute HCl to give a metal salt and H2 gas.

2Na + 2HCl → 2NaCl + H2  Hydrogen gas is not evolved when a metal reacts with nitric acid (HNO3)  As HNO3 is a strong oxidizing agent, it oxidizes the H2 to water and itself gets reduced to oxide of nitrogen (N2O, NO, NO2).  Magnesium and Manganese react with very dil.HNO3 to give H2 gas. Mg(s) + 2HNO3(aq) → Mg(NO3)2 + H2 Mn(s) + 2HNO3(aq) → Mn(NO3)2 + H2  Aqua regia, (Latin for ‘royal water’) is a mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It can dissolve gold, even though neither of these acids can do so alone. Aqua regia is a highly corrosive, fuming liquid. It is one of the few reagents that is able to dissolve gold and platinum.

Activity Series of Metals:  Reactivity of metals is related to their tendency to form cations by losing one or more electrons. Thus a more Thread electropositive metal is more reactive.  The arrangement of metals in a vertical column in the iron nail order of decreasing reactivity is called the “Reactivity series of metals”.  Reactive metals can displace less reactive metals from Copper their compounds in their solution or molten form. Sulphate  All metals are not equally reactive. Displacement solution reactions give better evidence about the reactivity of metals. It is simple and easy if metal A displaces metal B from its solution. The metal A is more reactive than metal B.

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Thread Copper wire Iron Sulphate solution

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48

Metal A + Salt solution of B → Salt solution of A + Metal B

More reactive than hydrogen Reactivity greater than 1

Reactivity = 1 Reference Less reactive than hydrogen Reactivity less than 1

Metal Symbol K Na Ca Mg Al Zn Fe Ni Sn Pb (H) Cu Hg Ag Au

Name Potassium Sodium Calcium Magnesium Aluminium Zinc Iron Nickel Tin Lead Hydrogen Copper Mercury Silver Gold

Most reactive metal

Chemical reactivity of metals decreases from top to bottom

Least reactive metal

 More reactive metals can displace less reactive metals from their solutions. Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)

How do metals and non-metals react? 

We know that noble gases, which have completely filled valence shell, show little chemical activity. We, therefore, explain the reactivity of elements as a tendency to attain a completely filled valence shell. Number of electrons in shells Type of Atomic Element element number K L M N

Noble gases

Metals

Non-metals

48

Helium (He)

2

2

Neon (Ne)

10

2

8

Argon (Ar) Sodium (Na)

18 11

2 2

8 8

8 1

Magnesium (Mg)

12

2

8

2

Aluminium (Al)

13

2

8

3

Potassium (K)

19

2

8

8

1

Calcium (Ca)

20

2

8

8

2

Nitrogen (N)

7

2

5

Oxygen (O)

8

2

6

Fluorine (F)

9

2

7

Phosphorus (P)

15

2

8

5

Sulphur (S)

16

2

8

6

Chlorine (Cl)

17

2

8

7


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We can see from the Table below that a sodium atom has one electron in its outermost shell. If it loses the electron from its M shell then its L shell now becomes the outermost shell and that has a stable octet.  The nucleus of this atom still has 11 protons but the number of electrons has become 10, + so there is a net positive charge giving us a sodium cation Na . On the other hand chlorine has seven electrons in its outermost shell and it requires one more electron to complete its octet. If sodium and chlorine were to react, the electron lost by sodium could be taken up by chlorine.  After gaining an electron, the chlorine atom gets a unit negative charge, because its nucleus has 17 protons and there are 18 electrons in its K, L and M shells. This gives us a chloride – anion Cl . So both these elements can have a give-and-take relation between them as follows.  Formation of sodium chloride Na

→ [Na ] + +

Cl

+

Cl

Na → Na + e

Cl + e → Cl

2,8,1

2, 8, 7

+

–

–

2,8

–

2, 8, 8

(Sodium cation)

(Chloride anion)

 Sodium and chloride ions, being oppositely charged, attract each other and are held by strong electrostatic forces of attraction to exist as sodium chloride (NaCl). It should be noted that sodium chloride does not exist as molecules but aggregates of oppositely charged ions.  Let us see the formation of one more ionic compound, magnesium chloride. Mg → Mg

2+

2,8,2

Cl + e → Cl−

–

–

+ 2e

2,8

2, 8, 7

2, 8, 8

(Magnesium cation)

(Chloride anion)

Cl Mg

→ [Mg ] 2+

+

Cl 2

Cl  The compounds formed in this manner by the transfer of electrons from a metal to a non-metal are known as ionic compounds or electrovalent compounds. 2+ –  The cation is Mg and the anion is Cl in the compound MgCl2.

Properties of Ionic Compounds: Melting point (K)

Boiling point (K)

NaCl

Ionic compound

1074

1686

LiCl

887

1600

CaCl2

1045

1900

CaO

2850

3120

MgCl2

981

1685



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Below is enlisted some general properties of ionic compounds  Physical nature: Ionic compounds are solids and are somewhat hard because of the strong force of attraction between the positive and negative ions. These compounds are generally brittle and break into pieces when pressure is applied.  Melting and Boiling points: Ionic compounds have high melting and boiling points (see Table above) this is because a considerable amount of energy is required to break the strong inter-ionic attraction. Universal Tutorials – X CBSE (2012–13) – Chemistry

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50 

Solubility: Electrovalent compounds are generally soluble in water and insoluble in solvents such as kerosene, petrol, etc.  Conduction of Electricity: The conduction of electricity through a solution involves the movement of charged particles. A solution of an ionic compound in water contains ions, which move to the opposite electrodes when electricity is passed through the solution. Ionic compounds in the solid state do not conduct electricity because movement of ions in the solid is not possible due to their rigid structure. But ionic compounds conduct electricity in the molten state. This is possible in the molten state since the electrostatic forces of attraction between the oppositely charged ions are overcome due to heat. Thus, the ions move freely and conduct electricity.

Occurrence of metals: 

The naturally occurring compounds of a metal mixed with earthy materials (impurities) are called minerals.

Ores: 

A mineral from which metals can be extracted profitably on a commercial basis is called an ore.  For eg: Aluminium occurs in earth’s crust in the form of two minerals bauxite and clay out of which Aluminium can be conveniently extracted from bauxite and not from clay. Therefore, ore of Aluminium is bauxite.

Abundance of metal in the earth’s crust: 

(in decreasing order of occurrence)  Al (Aluminium)  Fe (Iron)  Ca (Calcium)  Na (Sodium)  K (Potassium)  Mg (Magnesium)  Ti (Titanium)  All other metals are present to a much smaller extent.



Which is the most abundant metal? Ans: Aluminium is the most abundant metal in the earth’s crust.

Metallurgy:  Extraction of metals from their ores and refining them for use is called “Metallurgy”.  Some metals are found in the earth’s crust in the Free State. Some are found in the form of their compounds. The metals at the bottom of the activity series are the least reactive.  Least reactive metals are often found in the Free State. For example, gold, silver, platinum and copper are found in the Free State. Copper and silver are also found in the combined state as their sulphide or oxide ores.  The metals at the top of the activity series (K, Na, Ca, Mg and Al) are so reactive that they are never found in nature as free elements.  The metals in the middle of the activity series (Zn, Fe, Pb, etc.) are moderately reactive. They are found in the earth’s crust mainly as oxides, sulphides or carbonates. You will find that the ores of many metals are oxides. This is because oxygen is a very reactive element and is very abundant on the earth. 50


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 Thus on the basis of reactivity, we can group the metals into the following three categories  Metals of low reactivity  Metals of medium reactivity  Metals of high reactivity.  Different techniques are to be used for obtaining the metals falling in each category.  Several steps are involved in the extraction of pure metal from ores. A summary of these steps is given. Each step is explained in detail in the following sections.

Metals of high reactivity ↓ Electrolysis of molten ore ↓ Pure metal

Ore ↓ Concentration of ore ↓ Metals of medium reactivity ↓ Carbonate ore Sulphide ore ↓ ↓ Calcination Roasting

Metals of low reactivity ↓ Sulphide ores ↓ Roasting ↓ Metal Oxide ↓ Reduction of metal oxides ↓ Purification of metal

↓ Oxide of metal ↓ Reduction of metal oxides ↓ Purification of metal Steps involved in the extraction of metals from their ores

Note: The unwanted impurities present in a metal ore are called gangue e.g. sand, lime-stone etc. Metals found in native state are Au, Ag, Pt. Extraction of metal from the concentrated ore: 

Conversion of concentrated ore to metal oxide by calcination or roasting  Reduction of the oxide to the metal by electrolysis or using reducing agents Refining of the metal: (Purification) 

Electrolysis (electrolytic refining) POWDERED ORE

Enrichment of Ores: 

Ores mined from the earth are usually contaminated with large amounts of impurities such as soil, sand, etc., these impurities are called gangue.  The impurities must be removed from the ore prior to the extraction of the metal.  The processes used for removing the gangue from the ore are based on the differences between the physical or chemical properties of the gangue and the ore.  Different separation techniques are accordingly employed.

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GANGUE SUSPENSION OF THE ORE WATER


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Conversion to Metal Oxide:  It is easier to obtain metals from their oxides (by reduction) than from carbonates or sulphides. So, before reduction: the ore must be converted into metal oxide.  A Carbonate ore is converted into oxide by “Calcination”.  A Sulphide ore is converted into oxide by “Roasting”.

Extracting Metals Low in the Activity Series: 

Metals low in the activity series are very unreactive. The oxides of these metals can be reduced to metals by heating alone. For example, cinnabar (HgS) is an ore of mercury. When it is heated in air, it is first converted into mercuric oxide (HgO). Mercuric oxide is then reduced to mercury on further heating. heat (Roasting) 2HgS(s) + 3O2(g)     → 2HgO(s) + 2SO2(g) heat 2HgO(s)  → 2Hg(l) + O2(g)



Similarly, copper which is found as Cu2S in nature can be obtained from its ore by just heating in air. heat (Roasting) 2Cu2S + 3O2(g)     → 2Cu2O(s) + 2SO2(g) heat 2Cu2O  → 4Cu(s) + O2(g)

1. Calcination: 

The process in which ore is heated in the absence of air or limited supply of air is called “Calcination”. Ores are calcined to  Convert a carbonate ore to metal oxide  Remove water from hydrated ores  Remove volatile impurities (converted into vapours e.g. As, Sb etc.) from the ore.



General reaction: M2(CO3)x → M2Ox + CO2↑



Example:

Calcination ZnCO3   → ZnO + CO2

Zinc Carbonate (Calamine Ore)

Zinc Oxide

2. Roasting: 

The process in which ore is heated in the presence of air is called as “Roasting”. Ores are roasted to:  Convert a sulphide ore to metal oxide. To remove volatile impurities



General reaction:

∆ 2M2Sx + 3O2 → 2M2Ox + xSO2

Example:

∆ 2ZnS + 3O2 → 2ZnO + 2SO2

Comparison between Calcination and Roasting: Calcination

Roasting 2–

Used for CO32 − ores

Used for S ores

Ore is heated in the absence of air

Ore is heated in the presence of air

Done to expel CO2 from carbonate ores

Done to expel SO2 from sulphide ores.

Extracting Metals in the Middle of the Activity Series: 

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The metals in the middle of the activity series such as iron, zinc, lead, copper, etc. are moderately reactive. These are usually present as sulphides or carbonates in nature. Universal Tutorials – X CBSE (2012–13) – Chemistry

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

It is easier to obtain a metal from its oxide, as compared to its sulphides and carbonates. Therefore, the metal sulphides and carbonates must be converted into metal oxides.  The sulphide ores are converted into oxides by heating strongly in the presence of excess air. This process is known as roasting.  The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination. The chemical reaction that takes place during roasting and calcination of zinc ores can be shown as follows: Roasting: 

heat 2ZnS(s) + 3O2(g)  → 2ZnO(s) + 2SO2(g)

Calcination: 

heat ZnCO3(s)  → ZnO(s) + CO2(g)



The metal oxides are then reduced to the corresponding metals by using suitable reducing agents such as carbon. For example, when zinc oxide is heated with carbon, it is reduced to metallic zinc.  ZnO(s) + C(s) → Zn(s) + CO(g)  Besides using carbon (coke) to reduce metal oxides to metals, sometimes displacement reactions can also be used. The highly reactive metals such as sodium, calcium, aluminium, etc., are used as reducing agents because they can displace metals of lower reactivity from their compounds. For example, when manganese dioxide is heated with aluminium powder, the following reaction takes place  3MnO2(s) + 4Al(s) → 3Mn(l) + 2Al2O3(s) + Heat  These displacement reactions are highly exothermic. The amount of heat evolved is so large that the metals are produced in the molten state. In fact, the reaction of iron(III) oxide (Fe2O3) with aluminium is used to join railway tracks or cracked machine parts. This reaction is known as the thermite reaction.  Fe2O3(s) + 2Al(s) → 2Fe(l) + Al2O3(s) + Heat

Reduction:  The production of a metal from its metal oxide is called Reduction. The method, by which the metal oxide is to be reduced, depends on the nature of metal oxide and the impurities present in it.

1. Reduction of Metal Oxide to Metal: 

The method used depends on the chemical reactivity of the metal being extracted. Some of the methods used are:  Reduction by heat alone.  Electrolytic Reduction

2. Reduction by heat alone: 

The oxides of comparatively un-reactive metals that are quite low in the reactivity series can be reduced to metals by the action of heat alone.  Example: Mercury metal is produced from its sulphide ore called cinnabar (HgS) Roasting 2HgS (cinnabar ore) + 3O2  → 2HgO + 2SO2↑

(Mercuric sulphide ore)

(from air)

(Mercuric oxide)

Heat / Re duction 2HgO (Mercuric oxide)    → 2Hg + O2↑

Note: In extraction of mercury metal from cinnabar ore, the process of roasting and reduction go on side by side. Volume


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Reduction by Carbon: 

Metal oxides are reduced by carbon. The process of extracting a metal by fusion of metal oxide ore with carbon is called Smelting.

General Reaction: ZnO

+

(Zinc Oxide)

C

→

Zn

(Carbon)

+

CO↑

Zinc Metal

(reducing agent)

Reduction by Aluminium (Thermite Process): 

Some metal oxides are not satisfactorily reduced by carbon. They are high up in the reactivity series and are very reactive. Then a more reactive element like Al is used as a reducing agent. This is called aluminothermy or thermite reaction. 3MnO2

+

4Al

→

3Mn

+

(Manganese dioxide) (Al powder) (Molten Metal)

2Al2O3 (reducing

agent)

Thermit process for joining railway tracks

Note: 1) These reactions are highly exothermic - Produce metals in molten state 2) Can be used for welding metals. 3) This is also known as Goldschmidt thermite Process / Alumino thermite Process 4) Reaction of Fe2O3 with Al is used to join railway tracks or cracked machine parts Fe2O3(s) + 2Al(s) → 2Fe(l) + Al2O3(s)

Extracting Metals towards the Top of the Activity Series: Electrolytic reduction: 

The oxides of highly reactive metals like Al, Na, K, Mg and Ca that are high up in the reactivity series are very stable and cannot be reduced by chemical reduction using carbon or aluminium.  Hence they are reduced by electrolytic reduction since the positive ions are very stable and need a very powerful reducing agent. eg. the electron  Example: Sodium metal is extracted by the electrolysis of fused/molten NaCl. electrolysis 2NaCl(l)   →

Sodium Chloride (Molten)

2Na

Sodium Metal

+

Cl2↑ Chlorine gas



The metals high up in the reactivity series are very reactive. They cannot be obtained from their compounds by heating with carbon.  For example, carbon cannot reduce the oxides of sodium, magnesium, calcium, aluminium, etc., to the respective metals. This is because these metals have more affinity for oxygen than carbon. These metals are obtained by electrolytic reduction. For example, sodium, magnesium and calcium are obtained by the electrolysis of their molten chlorides.  The metals are deposited at the cathode (the negatively charged electrode), whereas, chlorine is liberated at the anode (the positively charged electrode). The reactions are: + – – –  At cathode Na + e → Na At anode 2Cl → Cl2 + 2e  Similarly, aluminium is obtained by the electrolytic reduction of aluminium oxide.

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Aqueous solution of sodium chloride cannot be used to obtain sodium metal, why? +

+

+

Ans: As current is passed through NaCl(aq) two cations are obtained simultaneously Na and H . As H + + ions have more tendency to undergo reduction than Na the H ions are reduced to form H2 + rather than Na . Thus at cathode H2 is obtained not Na. Hence the solution of sodium chloride cannot be used to obtain sodium metal. Fused NaOH is used instead.

Refining of Metals (Purification of Metals):  The method to be used for refining an impure metal depends on the following:  The nature of metal, and the nature of impurities present in it

Electrolytic refining (Purification by electrolysis): 

In this method of refining using electrolysis,  Metals like Cu, Zn, Ag and Au are refined.  Anode : Impure metal  Cathode : Strip of pure metal.  Electrolyte : Solution of metal salt.



Key Cathode

Anode Acidified copper sulphate Solution Impurities (anode mud)

Electrolytic Refining On electrolysis, impure metal from anode goes into the electrolyte and an equal amount of metal ions from the electrolyte get deposited on the cathode. Impurities are left behind and are collected as anode mud.

Differentiation between Cathode and Anode Cathode Cathode is a negatively charged electrode Cations (positive ions) are attracted towards cathode Reduction takes place at cathode + – Eg. M + e → M (M = any metal)

Anode Anode is a positively charged electrode Anions (negative ions) are attracted towards anode. Oxidation takes place at anode + – Eg. M → M + e (M = any metal)



Titanium, Chromium, Zirconium are called strategic metals, why?

Sol:

Because they are essential for a country‘s economy and defence.

Corrosion:  The process of slow conversion of metals into their undesirable compounds by reaction with moisture and other gases present in the atmosphere is known as corrosion.  Silver articles become black after some time when exposed to air. This is because it reacts with sulphur in the air to form a coating of silver sulphide.  Copper reacts with moist carbon dioxide in the air and slowly loses its shiny brown surface and gains a green coat. This green substance is copper carbonate.  Iron when exposed to moist air for a long time acquires a coating of a brown flaky substance called rust.  When the surface of a metal is attacked by air, water or any other substance around it. It is said to corrode and this phenomenon is known as corrosion.  Sometimes it is advantageous as it prevents the metal underneath from further damage.  Eg.: On exposure to air, the surface of aluminium is coated with a thin layer of aluminium oxide. Volume


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 Composition of rust: Fe2O3, xH2O or

Fe2O3 . Fe(OH)3.

Examples of corrosion: 

Rusting of iron.  Lead loses its lustre.  Silver gets tarnished.  Copper develops green coating on its surface.  Conditions under which iron rusts

In test tube A: 

Air

Put some water and cork it

In test tube B: 



Rusty Iron nails

Pour boiled distilled water, then pour about 1 ml oil and cork it. The oil will float on water and prevent air from entering

Water

A

In test tube C:

Dry air

Air

B

Layer of oil (prevents) air dissolving in the water) Boiled distilled Water (boiled to remove any dissolved air)

Anhydrous Calcium Chloride (drying

C

Put some anhydrous calcium chloride which will absorb moisture and cork it.  Take the 3 test tubes add clean iron nails in each of them.  You will observe nails rust in test tube A.  This shows both air and water is necessary for iron to rust.

Prevention of corrosion:  



  





Rusting of iron can be prevented by painting, oiling and greasing, galvanising, chrome plating, anodizing or making alloys. Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc. The galvanised article is protected against rusting even if the zinc coating is broken. This is because zinc is more reactive than Iron (Higher up in position in electro chemical series). Hence it gets oxidized to ZnO faster than iron thus protecting the underlying iron metal from corrosion or oxidization. Alloying is a very good method of improving the properties of a metal. We can get the desired properties by this method. Iron is the most widely used metal. But it is never used in its pure state. This is because pure iron is very soft and stretches easily when hot. But, if it is mixed with small amounts of carbon (about 0.05%), it becomes hard and strong. When iron is mixed with nickel and chromium, we get stainless steel, which is hard and does not rust. Thus, if iron is mixed with some other substance, its properties change. The properties of any metal can be changed if it is mixed with some other substance. The substance added may be a metal or a non-metal. An alloy is a homogeneous mixture of two or more metals, or a metal and a nonmetal. It is prepared by first melting the primary metal, and then, dissolving the other metal or nonmetal elements in it in definite proportions. It is then cooled to room temperature.

Alloys:     56

An “Alloy” is a uniform mixture of one metal with one or more metals or non-metals. Alloys have properties different from those of the constituent metals Alloys can be made to possess desired properties Alloys are homogeneous. Universal Tutorials – X CBSE (2012–13) – Chemistry

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 Most of the commercial metals that you see are alloys consisting of one metal with small quantities of some other metals.  Electric conductivity of an alloy is less than that of pure metals.  For example, brass, an alloy of copper and zinc (Cu and Zn), and bronze, an alloy of copper and tin (Cu and Sn), are not good conductors of electricity whereas copper is used for making electrical circuits.  Solder an alloy of lead and tin (Pb and Sn), has a low melting point and is used for welding electrical wires together.  Alloy has lower melting point than any of its constituents.  If one of the metals is mercury, the alloy is known as amalgam.  Amalgam is normally used as a reducing agent during chemical reactions e.g. Na – Hg.  Purpose of making amalgam of metals like Na, Zn is to lower their reactivity. Alloy

Constituents

Properties

Uses

Steel

Fe, C

Hard, tough and strong

Construction of ships, buildings and vehicles.

Stainless Steel

Fe, Ni, Cr

Hard and does not rust

Surgical instruments, cutlery, utensils etc.

Brass

Cu, Zn

Malleable, strong, resists corrosion.

Utensils, equipment for feed and dairy industry

Steel: General Properties: Percentage of carbon

1.1 to 1.5

Melting point

1300° – 1400°C

Malleability

Brittle and malleable

Structure

Crystalline

Hardness

Neither hard nor soft

Magnetisation

Magnetised permanently

Tempering

Can be tempered

Welding

Can be welded

Characteristic properties of steels: Alloy steel

Nickel steel

Chromium steel

Manganese steel

Tungsten steel

Stainless steel

Composition

3.5% Nickel

1.5 to 2% Chromium

12 to 15 % Manganese

14 to 20% Tungsten

Chromium with little nickel

Nature

Very tough, elastic, resists rusting

Extremely hard

High tenacity, resist wear and tear

Extremely hard & strong

Does not corrode

Uses

Armour plates, aeroplanes, automobile parts, cables

Machinery, cutting tools

Helmets, body guards, rails, safes

High speed machinery

Articles used in kitchen

Uses of Steel:  

Manufacture of rails, locomotives, war implements, surgical instruments and cutlery. Tempered steel is used in the manufacture of watch springs, razor blades etc.

Alloying of Gold:  Pure gold is known as 24 carat gold and is very soft and not suitable for making jewellery. 22 carat means 22 parts of 24 by mass is gold and rest is either Ag or Cu. Volume


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 Gold jewellery is made from an alloy that is a solid solution of gold containing some silver.  Pure gold is too soft for jewellery; the alloy is much harder.

Non Metals: Importance:  Non Metals: 22 Gases: 11 Solids: 10 Liquid: 1  Non-metals though small in number are the major constituents of air, ocean and earth.  The major non-metals in the earth’s crust in order of their abundance are oxygen, silicon, phosphorus and sulphur.  They form negative ions by gaining electrons. They have properties opposite to those of metals.

Chemical Properties of Non Metals: 1) With Oxygen: 

They form covalent oxides with oxygen e.g. carbon and sulphur. C + O2 → CO2 S + O2 → SO2

2) With Acid: 

Non-metals do not displace hydrogen from dilute acids.  Eg: C or S does not react with dilute acids. Hydrogen can only be displaced from dilute + acids if electrons are supplied to H ions of acid. +  A non metal is an electron acceptor. It cannot supply H ions. So it does not displace hydrogen from dilute acids.

3) With Water: 

Some of the above oxides of non-metals form acids on dissolution in water. CO2 + H2O → H2CO3

(Carbonic acid)

SO2 + H2O → H2SO3 (Sulphurous acid)  Other oxides like CO, N2O etc are neutral. APPENDIX: NCERT ACTIVITIES Activity 3.1: Aim: To show that metals have a metallic lustre. Apparatus: Samples of iron, copper, aluminium and magnesium. Procedure: Take samples of iron, copper, aluminium and magnesium. Note the appearance of each sample. Clean the surface of each sample by rubbing them with sand paper and note their appearance again. Observation: We observe that the metals have a shinning surface. Conclusion: Metals have a metallic lustre. Activity 3.2: Aim: To show that metals have varying hardness. Apparatus: Small pieces of iron, copper, aluminium, magnesium and sodium 58


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Procedure: Take small pieces of iron, copper, aluminium, and magnesium. Try to cut these metals with a sharp knife. Hold a piece of sodium metal with a pair of tongs. Put it on a watchglass and try to cut it with a knife. Observation: We observe that the iron, copper, aluminium, magnesium is difficult to cut while sodium cuts easily with a knife. Conclusion: Metals are generally hard. The hardness varies from metal to metal. Activity 3.3: Aim: To show that metals are malleable. Apparatus: Pieces of iron, zinc, lead and copper. Procedure: Take pieces of iron, zinc, lead and copper. Place any one metal on a block of iron and strike it four or five times with a hammer. Repeat with other metals. Record the change in the shape of these metals. Observation: We observe that the metals can be beaten into thin sheets. Conclusion: Metals are generally malleable. This property is called malleability. Gold and silver are the most malleable metals. Activity 3.4: Aim: To show that metals are ductile. Apparatus: iron, copper, aluminium, lead. Procedure: Take pieces of iron, copper, aluminium, lead and draw them into fine wires. Observation: We observe that some metals can be drawn into fine wires. Conclusion: Metals are generally ductile. This property is called ductility. Gold is the most ductile metal. A wire of about 2 km length can be drawn from 1 gm of gold. Activity 3.5 (a): Metal wire Aim: To show that metals are good conductors of heat and have high melting points. Pin Apparatus: aluminium or copper wires, burner, wax, pin, battery clips, Wax bulb. Procedure: Take an aluminium or copper wire. Clamp this wire on a stand, Fix a pin to the free end of the wire using wax. Heat the wire with a spirit lamp, candle or a burner near the place where it is clamped. Observation: We observe that the wax melts and pin drops off because metals are good conductors of heat and they have allowed heat to travel through them to melt the wax. They have also high melting points. Conclusion: Metals are good conductors of heat and have high melting points. The best conductors of heat are silver and copper. Lead and mercury are comparatively poor conductors of heat. Activity 3.5 (b): Bulb Aim: To show that metals are good conductors Battery of electricity. Procedure: Set up an electric circuit as shown in Fig. Place the metal to be tested in the circuit Clips between terminals A and B as shown. Does the A B bulb glow? What does this indicate? Insert sample to be tested Observation: The bulb glows because electricity is passing through its filaments. This indicates that metals are good conductors of electricity. Volume


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Activity 3.6: Aim: To show that non–metal oxides are acidic in nature while metal oxides are basic in nature. Apparatus: magnesium ribbon and some sulphur powder, test tube, burner, blue and red litmus papers. Procedure: Take a magnesium ribbon and burn the magnesium ribbon. Collect the ashes formed and dissolve them in water. Test the resultant solution with both red and blue litmus papers. Now burn sulphur powder, place a test tube over the burning sulphur to collect the fumes produced. Add some water to the above test tube and shake. Test this solution with blue and red litmus papers. Observation: We observe that SO2(aq) turns blue litmus paper red. Thus most non–metals produce acidic oxides when dissolved in water. On the other hand MgO(aq) turns red litmus paper blue. Thus most metals, give rise to basic oxides. Conclusion: Generally non–metal oxides are acidic in nature while metal oxides are basic in nature. ∗Please note that some non-metal oxides are neutral in nature e.g. H2O, NO2, while certain metallic oxides e.g. Al2O3, ZnO, PbO are amphoteric in nature. Activity 3.7: Aim: To show properties of non–metals. Apparatus: Carbon, sulphur iodine Procedure: perform procedures of activities 3.1; 3.2; 3.3; 3.4; 3.5 (a) and (b) on the above mentioned elements (non–metals) Observation: Element

Symbol

Carbon Coal Graphite Sulphur Iodine

C

S I

Type of surface Rough Smooth Rough Smooth

Hardness

Malleability

Ductility

Hard Soft Soft Soft

No No No No

No No No No

heat

Conduction electricity

Bad Bad Bad Good

Bad Good Bad Good

Sonority

No No No No

Conclusion: thus from the above experiments we come to know about certain properties of metals and non–metals. Activity 3.8: Aim: To show that metals react differently with dil. HCl. Apparatus: Mg, Zn, Fe, Al, Cu, dil. HCl, test tubes, burner, thermometers. Procedure: Collect all the metal samples and if they are tarnished, rub them clean with sand paper. Put the Mg, Zn, Fe, Al, Cu, separately in test tubes containing dilute hydrochloric acid. Suspend thermometers in the test tubes, so that their bulbs are dipped in the acid. Observation: We observe that hydrogen gas is evolved in all the cases and were fastest in the case of Mg. The reaction was also the most exothermic in this case. The reactivity decreases in the order Mg > Al > Zn > Fe. In the case of copper, no bubbles were seen and the temperature also remained unchanged. This shows that copper does not react with dilute HCl. Conclusion: This shows that metals react differently with dil. HCl. Activity 3.9: Aim: To show that reactive metals can displace less reactive metals from their compounds in solution or molten form. Apparatus: Wire of copper, iron nail, Iron sulphate solution, Copper sulphate solution and test tubes. 60


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Procedure: Take a clean wire of copper and an iron nail. Put the copper wire in a solution of iron sulphate and the iron nail in a solution of copper sulphate taken in different test tubes. Record your observations after 20 minutes. Observation: We observe that in the test tube containing iron and copper sulphate solution a chemical reaction has occurred and the colour of copper sulphate has changed from blue to colourless and the iron nail has turned black. But in the test tube containing iron sulphate and copper no chemical reaction takes place. The colour of FeSO4 solution remains the same (pale green). Conclusion: This shows that (i) reactive metals can displace less reactive metals from their compounds in solution or molten form i.e. Fe displaces copper from CuSO4 solution to form FeSO4 and Cu because Fe is more reactive than Cu. Hence in the second case no reaction takes place (ii) All metals are not equally reactive (iii) The reaction that has taken place is displacement reaction because iron displaces copper from copper sulphate solution and FeSO4 was formed. This is shown by the following chemical reaction, Fe + CuSO4 → FeSO4 + Cu Activity 3.10: Aim: To study the properties of ionic compounds. Apparatus: Samples of sodium chloride, potassium iodide, barium chloride or any other salt, battery, bulb, switch, beaker, graphite rod, petrol, kerosene, water, burner and a metal spatula. Procedure: Take samples of sodium chloride, potassium iodide, barium chloride or any other salt. These are all solids. Take a small amount of a sample on a metal spatula and heat it directly on the flame. Repeat with other samples. Make a circuit as shown in the second figure along side and insert the electrodes into a solution of any one salt. Test the other salt samples too in this manner. Try to dissolve the samples in water, petrol or kerosene. Also place each solid compound in the electrical circuit and observe what happens. Observation: We observe (i) NaCl burns with a golden flame KI burns with a lilac coloured flame BaCl2 burns with an apple green flame (ii) The samples are soluble in water but insoluble in petrol and kerosene (iii) These samples conduct electricity in the molten state, but in a solid state they did not conduct electricity. Conclusion: Thus (i) ionic compounds have high bp and mp (ii) they are soluble in water and insoluble in organic solvents (iii) They are good conductors of electricity. REVIEW QUESTIONS: CLASS WORK Very Short Answer: 1 Mark 1) Aluminium occurs as a compound whereas gold is found in free state. Why? (1995) 2) An element X on reacting with oxygen forms an oxide X2O. This oxide dissolves in water and turns blue litmus red. State whether element X is a metal or a non-metal (1996) 3) What are the constituents of an alloy called ‘stainless steel’? (1996) 4) Name one metal element and one non-metal element which are obtained on a large scale generally from seawater. (1997) 5) Identify the most reactive and the least reactive metal amongst the following: Al, K, Cu and Au. Volume


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6) Write the constituents of Brass. (1997) 7) What is Aqua regia? (1998) 8) What are metals? 9) Define the term metallurgy. 10) What is a thermite reaction? 11) Name one metal and non metal which are in the liquid state at room temperature. 12) Why are Zn, Ti and Cr classified as strategic metals? 13) Name two metals which occur in nature in the free state. 14) Identify the most reactive and least reactive metal from Hg, Na, Fe and Ag. 15) What is Aqua regia used for? 16) Name two metal oxides. 17) Which one of the given metals is a) least reactive b) most reactive K, Ag, Fe and Al 18) Name two metals which are soft and can be cut with a knife. 19) Which among Na and Al is more metallic? 20) Name a i) non–metal ii) and a metal which cannot be kept in air. 21) What is gangue? Short Answers: 2 – 3 Marks 22) On the basis of electron exchange define i) metals ii) non–metals. Support your answer by an example of each. 23) What is stainless steel? What is its composition? 24) What is an alloy? Why is gold alloyed? Give two reasons? 25) On the basis of reactions below indicate which is the most reactive metal and which is the least reactive metal amongst zinc, Cu, and Fe. CuSO4(aq) + Fe → FeSO4(aq) + Cu(s) FeSO4(aq) + Zn(s) → ZnSO4(aq) +Fe(s) 26) When a Cu wire is left in AgNO3 solution, it is observed that the solution turns bluish green a) Explain this observation b) Write the balanced chemical equation to represent the change taking place. 27) By giving an example, explain the following terms used in metallurgy i) roasting ii) Calcination. 28) Which of the following elements given below yield a) neutral oxides b) amphoteric oxides? Support your answer by a suitable example. i) Mg ii) H iii) Zn iv) C 29) Write chemical equations to show what happens when MnO2 is heated with Al. 30) Write chemical equations for the reactions taking place when i) Cinnabar (Hgs) is heated in air. ii) Ca reacts with H2O. 31) Give reasons for the following: i) ZnO is considered an amphoteric oxide. ii) Non–metals in general do not displace H from dilute acids. iii) Metals conduct electricity. 32) Name with examples three common compound forms, in which metals occur in nature. Write the chemical equation for a metal reacting with a dilute acid to produce hydrogen gas. 33) An element reacts with O to form an oxide which dissolves in dilute HCl. The oxide formed also turns a solution of red litmus blue. Is the element a metal or a non metal? Explain it with the help of a suitable example. 34) In feed and dairy industry a strong alloy is used for making equipments. The same alloy is also used in making utensils. Name the alloy and give its composition. (1995) 35) A utensil made of brass was kept in a kitchen. After some days, the utensil lost its lustre due to a greenish layer on it. What could be the cause for this? (1995) 36) Explain why the surface of some metals acquire a dull appearance when exposed to air for a long time? 37) What are amphoteric oxides? Give examples of two amphoteric oxides. 38) Name two metals which do not react with oxygen. 62


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39) Which gas is produced when a metal reacts with dilute hydrochloric acid? Write the chemical reaction when iron reacts with dil. H2SO4. 40) What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place. 41) Does every mineral have a definite and fixed composition? Explain. 42) Differentiate between roasting and calcination. 43) Name the various processes used for the refining of metals. Which method is used for refining volatile metals? 44) What type of solution-acidic, basic or neutral is formed by dissolving the oxides of Group 1 in water? 45) What important properties of copper are responsible for its great demand in industry? 46) Why is iron more useful when it is mixed with a little carbon? 47) What is the difference between stainless steel and steel? 48) What is 24 carat gold? How will you convert it into 18 carat gold? 49) State two ways to prevent the rusting of iron. Differentiate between metals and non-metals. 50) What types of oxides are formed when non-metals combine with oxygen? 51) Water should never be added to conc. H2SO4. Why? 52) Give reasons: i) Metals displace hydrogen from dilute acids, whereas non-metals do not. ii) Carbonate and sulphide ores are usually converted into oxides. 53) Which two metals do not corrode easily? Give an example in each case to support that i) Corrosion of a metal is a serious problem. 54) Why does Fe displace Cu from CuSO4? What do you observe? 55) Zn and Al are very high in the chemical series. Yet they resist corrosion to a great extent. Explain 56) State the reason for the following behavior of Zn metal. On placing a piece of Zn metal in a solution of Hg2Cl2 it acquires a shining silvery surface but when it is placed in a solution of MgSO4 no change is observed. 57) Write chemical equations for the reactions taking place when i) Steam is passed over red hot iron ii) SO2 gas is dissolved in water. 58) Give reasons for the following i) Metals conduct electricity ii) Reactions of HNO3 with metals generally do not evolve H gas iii) For making gold ornaments, 22 carat gold is preferred over 24 carat gold. 59) Write chemical equations for the reactions taking place when i) ZnS is heated in air ii) CO2 is passed through lime water. 60) How are metalloids different from metals? Name a metalloid. 61) Give reasons for the following: i) Silicon is counted among metalloids ii) Carbon is not used for extracting Al from Al2O3 62) Write chemical equation for the reaction taking place when ZnCO3 is calcined 63) Write chemical equation for the reaction Fe2O3 is heated with Al powder 64) i) Give reasons for the following. Na, K and Ca metals form hydroxides by combination with H gas but most other metals do not ii) Al easily combines with O but still it can be used for making kitchen utensils or inspite of high reactivity Al can be used for making household utensils. 65) State reasons why Na metal is stored in bottles filled with kerosene oil. 66) Write chemical equations for the reactions taking place when a piece of Zn is placed in a solution of CuSO4. 67) Write a chemical equation for the following reaction taking place when ZnS is roasted Volume


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68) Give reasons for the following: i) Germanium is known as a metalloid ii) H gas is not evolved when HNO3 acid reacts with Zinc Long Answers: (5Marks) 69) What method of concentration of ore is preferred in the following case and why? When the ore has higher density particles interspersed with a large bulk of low density impurities 70) Give an example of an amalgam 71) Define an alloy and an amalgam. State the main constituents of the following alloys. In what property is each one of them different from its main constituent i) stainless steel ii) Manganese steel. 72) What is galvanized iron? How is iron galvanized? What is the advantage of galvanising iron? State its two uses. 73) Why are ores and not minerals used for extraction of metals? 74) State the three major steps usually involved in metallurgical processes. REVIEW QUESTIONS: HOME WORK Fill in The Blanks: 1) With the exception of hydrogen all metals have one to _____electrons in their valence shell. 2) All non – metals have four to _____ electrons in their valence shell. 3) Active metals displace less _____ metals from their salt solutions. 4) Non – metals form _____ or acidic oxides. 5) An ore is a _____ from which a metal can be profitably and easily extracted 6) The chemical method for the concentration of an ore is followed when the _____ of the ore and gangue is almost same. 7) Purity of gold is measured in _____ State whether the statements given below are True or False: 8) Calcination is a process of heating concentrated ore in the presence of air. 9) Smelting is the process of conversion of concentrated ore into metals by the conventional reducing agents. Very Short Answer: 1 Mark 10) What is meant by malleability? 11) What is meant by ductility? 12) Write an equation for the reaction of Potassium with water 13) Which process is used for enrichment of (a) Sulphide ores (b) Oxide ores 14) Name a metal that is not corroded in air. 15) Name a non-metal which conducts electricity. 16) Which of the following metals would give H2 gas when added to dil. HCl? a) Iron b) Copper c) Magnesium 17) Which method is used for refining volatile metals? 18) Name the reducing agent in the following reaction. 3MnO2 + 4Al → 3Mn + 2Al2O3 19) Why are metals electropositive in nature 20) The atom of an element X has the electronic arrangement 2, 8, 18, 2. Without identifying the element, state the valency of the element and write whether it is likely to have oxidising or reducing properties. 21) What chemical process is used for obtaining a metal from its ore? 22) Define corrosion 64


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23) 24) 25) 26) 27) 28) 29) 30) 31) 32) 33) 34) 35) 36) 37) 38) 39) 40) 41) 42) 43) 44) 45) 46) 47) 48) 49) 50) 51) 52) 53) 54) 55) 56) 57) 58) 59) 60) 61) 62) 63) 64)

65

What is rust? Write its chemical formula? Name two elements that cannot be kept under water? What are non–metals? How many non metals have been discovered so far? Name two non–metals which have lustre and are good conductors of electricity What is the number of valence electrons in metals? Name a non–metal which forms positively charged ions. Towards which side of the periodic table are the non – metals located? Which among the given elements is a metal 11X; 14Y; 17Z? Which among the given elements is a non metal 9A; 10B; 12C How many non–metals exist in solid state? Give the names of three such non–metals +2 Complete the following equation Mg → Mg + _______ How can a chloride ion be changed to a chloride atom. ABCDE …….. J is the coded names of metals arranged in the order of increasing chemical reactivity. Identify i) most reactive ii) least reactive. –3 Name two metals whose density is less than 1gcm . Name a non–metal which is highly tensile. Name a naturally occurring non–metal which is the hardest substance Which one among the following is likely to form a cation? C, N, H, O Which one among the above is likely to form an anion? Name two metals which do not react with cold or boiling water but react with steam Name a metal which does not react with conc. HNO3. What happens when Cu is added to FeSO4? Name one metal i) which displaces Cu from CuSO4 solution ii) which does not displace Cu form CuSO4 solution Write an equation for the action of Na2O with water. Complete the statement: The white powder formed when Mg ribbon burns in oxygen is of _____ State reactions if any, for the following: Metals that react with CuSO4 solution i) Zn ii) Cu iii) Pt Name the non–metal which is included amongst metals regarding its chemical properties Name a non–metal which cannot be kept in air. Name two neutral non–metallic oxides. Name two acidic non–metallic oxides. What are two most important conditions for corrosion of metals? Name two factors which speed up the corrosion of metals State two ways of reducing or stopping the corrosion of metals Why does rusting cause a great economic loss every year? Metal A, B, ………, K represent metal activity series in decreasing order. Which metal is most likely to occur in free state in nature? Name two metals which can displace hydrogen from dil. HCl. In nature, metal A is found in free state, while metal B is found in the form of its compounds. Which of these two metals will be near the top of reactivity series? Which elements yield basic oxides? Metals are electropositive in nature. Why? Name the metal which burns in air with golden yellow flame. State two properties shown by metals, which are generally not shown by non–metals. Why are non–metals electronegative in nature?

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65) 66) 67) 68) 69) 70) 71)

Metals behave as reducing agents. Why? For the reduction of an oxide ore of a metal, suggest a reducing agent other than carbon. For the reduction of a non-metallic oxide, suggest a reducing agent other than carbon. For the reduction of a metallic oxide, suggest a reducing agent cheaper than aluminium. Describe the importance of coke in metallurgical processes. Give one difference between electrolytic reduction and reduction with carbon. Write a balanced chemical equation for the reaction between Aluminum and concentrated sulphuric acid. 72) Is it possible to store strong alkali solutions in an Aluminium container? Give one reason for your answer. 73) Aluminium is more active than iron, yet there is less corrosion of aluminium when both are exposed to air. Explain the statement. 74) Which metal foil is used in packaging medicine tablets? 75) Why does Aluminium not react with cold water under ordinary conditions? 76) Which elements are generally used for giving a coating to protect iron from rusting? 77) What are the main constituents of common brass? Short Answers: 2 – 3 Marks 78) How will you show that silver is less reactive than copper? 79) State two physical and one chemical reason for regarding potassium as a metal. 80) How does a metallic oxide differ from non – metallic oxide? Support your answer by an example. 81) State the name and formula of i) a covalent hydride ii) an electrovalent hydride 82) A piece of iron is in contact with Aluminium. Another piece of iron is in contact with copper. If both pieces are placed in moist air, which combination is likely to rust quickly and why? 83) Zinc is higher in electrochemical series than iron, yet it is used in preventing rusting of iron. Explain. 84) Which of the metals will react i) fastest ii) slowest with dilute sulphuric acid? Write fully balanced equations in support of your answer. 85) What does refining of metals mean? Name three methods used for refining metals. 86) You are given samples of three metals, sodium, magnesium and copper. Suggest any two activities to arrange them in the order of their decreasing reactivity. 87) How does activity series of metals help in predicting the relative reactivities of various metals? 88) A copper plate was dipped in silver nitrate solution after certain time; silver from solution was deposited on copper plate. State the reason why it happened? Give chemical equation for the reaction involved. 89) A zinc plate was kept in a glass container having copper sulphate solution. On examining it was found that blue colour of solution gets fainter and fainter. After few days zinc plate was taken out of the solution, and a number of holes were noticed in it. State the reason and give a chemical equation to support your answer. 90) Choose the metals and non–metals amongst the elements given below and state reasons for your choice: i) sodium ii) carbon iii) sulphur iv) magnesium 91) Explain why carbon can reduce copper oxide to copper, but not calcium oxide to calcium. 92) Write the electronic configuration of the element having atomic number 26. Where is it placed in the long form of the periodic table? 93) E is an element, which is one amongst Copper, Zinc, Aluminium and Iron. It shows the following properties. i) One of its ores is rich in E2O3. ii) E2O3 is not affected by water. iii) It forms two chlorides, ECl2 and ECl3. Which element is E? 66


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94) Define the term ‘alloy’. Write two advantages of making alloys. 95) Why do we make ‘alloys’? State any two reasons. 96) Name the alloys which are used for the following purposes. i) For soldering joints. ii) For making windows and floor fittings iii) For making equipments for food and diary industry. 97) Which of the following elements yield a) neutral oxides b) amphoteric oxides? Support your answer by suitable equations. i) Magnesium ii) Hydrogen iii) Carbon iv) Zinc Name two metals which are commonly used for alloying gold. 98) i) Name the unit in which purity of gold article is measured. ii) A sample of gold is 74.998% pure. Express the purity in terms of the unit named by you. 99) Give one example of each article made from iron, which is protected from rusting by: i) red lead paint ii) enamelling iii) plastic coating iv) tinning v) electroplating vi) oiling or greasing 100) Two elements A and B are stored under water and kerosene respectively. Name them 101) Draw a labelled diagram for electrolytic refining of copper, stating clearly on which electrode pure copper is collected. 102) Which one of the methods given in column I is applied for the extraction of each of the metals given in column II? Column I Column II i) Electrolytic reduction Aluminium and zinc ii) Reduction with carbon Sodium and iron iii) Reduction with aluminium Manganese and tin 103) Describe how pieces of broken iron girder can be joined by thermite welding. 104) What are minerals? State their importance in our body? Explain the specific function of any three minerals in the human body? 105) A, B and C are three elements which undergo chemical changes according to the equation: A2O3 + 2B → B2O3 + 2A; 3CSO4 + 2B → B2(SO4)3 + 3C; 3CO + 2A → A2O3 + 3C Arrange the elements in the order of decreasing reactivity. 106) Write a short note on the reactivity series of metals 107) Name two oxides which are neither acidic nor basic. 108) Write the reaction with zinc and iron (II) sulphate. Long Answer: (5 Marks) 109) K; Na; Ca; Mg; Al; Zn; Fe; Sn; Pb; Cu; Hg; Ag; Au constitute metal reactivity series. Answer the following questions and write chemical equations in support of your answer. i) Name the metal which on heating reacts with steam, but the reaction is reversible. ii) Name a metal which burns with a yellow flame and reacts with cold water. iii) Name a metal which does not react with water or steam, but reacts with dilute HCl slowly. iv) Name a metal which does not react with cold water, but reacts with boiling hot water. v) Name a metal which does not react with water or HCl. 110) Explain the following in regard to extraction of metals from their ores: i) Metals at the top of reactivity series do not occur in free state in nature. ii) Finely powdered ore is mixed with suitable oil and water in the concentration of sulphide ores. iii) Sulphide ores need to be roasted after concentration. iv) Mercury can be obtained just by roasting the ore. v) Highly reactive metals are obtained by electrolytic reduction of their compounds. Volume


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111) Give reasons for the following: i) Metals such as copper and aluminium are used to carry electric current. ii) Gold and silver are used to make jewellery. iii) Mercury is used in thermometers. iv) Titanium is classified as a strategic element. v) Alloys are made by melting different metals. NCERT EXERCISE: 1) Give an example of a metal which i) is a liquid at room temperature ii) can be easily cut with a knife. iii) is the best conductor of heat iv) is a poor conductor of heat. 2) Explain the meaning of malleable and ductile. 3) Why is sodium kept immersed in kerosene oil? 4) Write equations for the reactions of i) Iron with steam ii) Calcium and potassium with water 5) Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows. Metal Iron (II) sulphate Copper (II) sulphate Zinc sulphate Silver nitrate A No reaction Displacement –– –– B Displacement –– No reaction –– C No reaction No reaction No reaction Displacement C No reaction No reaction No reaction No reaction Use the Table above to answer the following questions about metals A, B, C and D. i) Which is the most reactive metal? ii) What would you observe if B is added to a solution of Copper(II) sulphate? iii) Arrange the metals A, B, C and D in the order of decreasing reactivity. 6) Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4. 7) What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place. 8) i) Write the electron-dot structures for sodium, oxygen and magnesium. ii) Show the formation of Na2O and MgO by the transfer of electrons. iii) What are the ions present in these compounds? 9) Why do ionic compounds have high melting points? 10) Define the following terms. i) Mineral ii) Ore iii) Gangue 11) Name two metals which are found in nature in the Free State. 12) What chemical process is used for obtaining a metal from its oxide? 13) Metallic oxides of zinc, magnesium and copper were heated with the following metals. Metal Zinc Magnesium Copper Zinc oxide Magnesium oxide Copper oxide In which cases will you find displacement reactions taking place? 14) Which metals do not corrode easily? 15) What are alloys? 68


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16) You are given a hammer, a battery, a bulb, wires and a switch. a) How could you use them to distinguish between samples of metals and non-metals? b) Assess the usefulness of these tests in distinguishing between metals and non-metals. 17) What are amphoteric oxides? Give two examples of amphoteric oxides. 18) Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it. a) What will be the action of the gas on (i) dry litmus paper? (ii) moist litmus paper? b) Write a balanced chemical equation for the reaction taking place. 19) State two ways to prevent the rusting of iron. 20) What type of oxide is formed when non-metals combine with oxygen? 21) Give reasons a) Platinum, gold and silver are used to make jewellery. b) Sodium, potassium and lithium are stored under oil. c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking. d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction 22) You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels. 23) Differentiate between metal and non-metal on the basis of their chemical properties. 24) A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used? 25) Give reasons why copper and not steel (an alloy of iron) is used to make hot water tanks. 26) Name two metals which will displace hydrogen from dilute acids, and two metals which will not displace it. 27) In the electrolytic refining of a metal M, name the anode, cathode and the electrolyte. MULTIPLE CHOICE QUESTIONS: PRACTICAL THEORY 1) The zinc metal used in the laboratory for doing experiments is available in the form of: a) Filings b) Strips c) Granules d) Pellets. 2) Which of the following is most reactive? a) Copper b) Aluminum c) Iron d) Zinc 3) When you place an iron nail in copper sulphate solution, the reddish brown coating formed on the nail is: a) Soft and dull b) Hard and flaky c) Smooth and shining d) Rough and granular 4) Zinc oxide is amphoteric because a) It reacts only with NaOH b) It reacts only with HCl c) It reacts both with NaOH and HCl d) It does not react with NaOH and HCl 5) The correct reaction between zinc and hydrochloric acid is a) Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) b) Zn + HCl → ZnCl2 + H2 d) Zn(s) + HCl(l) → ZnCl2(g) + 2[H](g) c) Zn + 2HCl → ZnCl2 + 2[H] 6) Which of the following is least reactive? a) Aluminum b) Zinc c) Copper d) Iron 7) When you place an iron strip in a solution of copper sulphate the time required for the colour of the solution to change from blue to colourless is about a) A second b) An hour c) 8 hours d) 24 hours Volume


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8) The figures below show set – ups for studying the reaction of zinc with sodium hydroxide

9) 10)

11)

12) 13) 14)

15)

16) 17)

18)

19)

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A rapid evolution of hydrogen gas will be observed in the test tube: a) I b) II c) III d) IV On adding aluminum to zinc sulphate solution, its colour becomes: a) Colourless b) White c) Blue d) Red 10 ml of freshly prepared iron sulphate was taken in each of four test tubes. Strips of copper, iron, zinc and aluminum were introduced, in different test tubes. A black residue was obtained in two of them. The right pair of metals forming the precipitate is: a) Copper and zinc b) Aluminum and copper c) Iron and aluminum d) Zinc and aluminum Gas produced on adding steam to Zn metal is: a) Hydrogen b) Oxygen c) Hydrogen and oxygen d) None of these Which of the following gases turns lime water milky? a) Hydrogen b) Oxygen c) Carbonmonoxide d) Carbondioxide Which one of the following is a light green solution? a) Iron sulphate b) Zinc sulphate c) Copper sulphate d) Aluminum sulphate An iron nail was suspended in copper sulphate solution and kept for a while. The solution: a) Became dark coloured and a coating was formed on the nail b) Turned green and a coating was formed on the nail c) Remained blue and no coating was formed on the nail d) Turned green and no coating was formed on the nail Which one of the following is a colourless solution? a) Zinc sulphate b) Aluminium sulphate c) Sodium sulphate d) All of them On adding copper to zinc sulphate the colour of solution: a) Becomes green b) Becomes blue c) Remains same d) Becomes colourless The gas produced on adding HCl to Zn metal is: a) Hydrogen b) Chlorine c) Hydrogen and chlorine d) None of these Which of the following is observed when granules of zinc are added to copper sulphate solution? a) The solution is blue in the beginning b) The final solution becomes colourless c) A brown mass is deposited in the solution of zinc sulphate d) All the above To show that zinc is more reactive than copper, the correct procedure is to: a) Prepare copper sulphate solution and dip zinc strip in it b) Prepare zinc sulphate solution and dip copper in it c) Heat zinc and copper strips d) Add dilute nitric acid on both strips. Universal Tutorials – X CBSE (2012–13) – Chemistry

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20) Presence of carbondioxide can be tested, because: a) CO2 turns red litmus blue b) It has a pungent odour c) CO2 turns lime water milky d) None of these 21) When zinc reacts with dilute hydrochloric acid: a) The surface of zinc becomes brighter b) The surface of zinc becomes dull c) The metal turns into powder d) The reaction mixture turns green 22) Which of the statements about the reaction below are incorrect? 2PbO(s) + C(s) → 2Pb(s) + CO2(g) i) Lead is getting reduced ii) Carbon dioxide is getting oxidized iii) Carbon is getting oxidized iv) Lead oxide is getting reduced a) (i) and (ii) b) (i) and (iii) c) (i) and (iv) d) all 23) Zinc granules were added to zinc sulphate, copper sulphate, aluminum sulphate and iron sulphate solutions as shown below. You would observe the deposition of metal in the beakers: Copper sulphate

Zinc sulphate

I)

Zinc

II)

Zinc

Aluminum. sulphate

III)

Zinc

………… ………… ………… ………… …… …… ………… …… IV) ………… ………… …… ………… .……… …… …… ………. …… …… ………. ………. ………. …………

Iron sulphate

Zinc

a) I and III b) II and IV c) I and II d) III and IV 24) Two beakers ‘A’ and ‘B’ contain an aqueous solution of FeSO4. In beaker ‘A’ a clean copper rod and in ‘B’, a zinc rod are placed respectively. It was found that grey coating was observed on zinc rod but not on copper rod. From the above observations the correct arrangement of Cu, Fe and Zn metals in the decreasing order of reactivity will be Cu

Zn

A

B FeSO4 Solution

a) Zn, Fe, Cu b) Fe, Zn, Cu c) Cu, Fe, Zn d) Zn, Cu, Fe 25) Which of the following metals displaces zinc from its solution of ZnSO4? a) Copper b) Iron c) Aluminum d) All of these 26) What is the effect of CO2 on moist litmus paper? a) It turns blue litmus paper red b) It turns red litmus blue c) No change in the litmus paper d) All of these 27) The correct equation for the reaction between zinc metal and sodium hydroxide is? ∆ ∆ a) Zn(s) + 2NaOH(aq) → Na2ZnO2(s) + H2(g)↑ b) 2Zn(s) + 2NaOH(aq) → Na2Zn2O2 + H2↑ ∆ c) Zn(s) + 2NaOH(aq) → Na2ZnO2(aq) + H2(g) d) None of these 28) Which of the following will not be observed when aluminium is added to a solution of copper sulphate? a) The solution is blue in the beginning b) The final solution becomes light green c) The final solution becomes colourless d) A brown mass is deposited on the surface of aluminium

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29) Four experimental sets are shown below:

30)

31) 32)

33) 34)

35)

36) 37) 38) 39)

40) 41)

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The set up that would result in a rapid evolution of a gas would be: a) I and III b) II and IV c) I and II d) III and IV In the reaction given below which element is more reactive? Zn + CuSO4 → ZnSO4 + Cu a) Zinc b) Sulphur c) Copper d) Oxygen Which of the following displaces copper from its solution of CuSO4? a) Zinc b) Iron c) Aluminum d) All of these Which statement regarding Aluminium is not true a) Aluminium is a very light metal b) Aluminium is a good conductor of electricity c) Aluminium forms acidic oxide only d) Aluminium reacts with nitrogen on heating A gas producing pop sound on burning with a blue flame is: a) Nitrogen b) Hydrogen c) Oxygen d) Carbondioxide Which of the following is observed when zinc, iron and copper are added to three different test tubes containing solutions of aluminum sulphate? a) A silver coloured mass is deposited on the surface of each metal b) The solution of aluminum sulphate becomes coloured c) Each test tube becomes hot d) No change takes place Which of the following pairs will give displacement reactions? i) NaCl solution and copper metal ii) MgCl2 solution and aluminium metal iii) FeSO4 solution and silver metal iv) AgNO3 solution and copper metal a) i and ii b) ii and iv c) iii and iv d) ii and iii A metal liquid at room temperature is a) Bromine b) Mercury c) Gallium d) None of these Gas produced on adding NaOH to Zn metal is: a) Nitrogen b) Hydrogen c) Oxygen d) Carbondioxide Which of the following is a blue coloured solution: a) CuSO4 b) FeSO4 c) ZnSO4 d) Al2(SO4)3 Four test tubes A, B, C and D are filled one third each respectively with aqueous solutions of ZnSO4, CuSO4, FeSO4 and Al2(SO4)3 respectively. Clean zinc metal strips are put in each test tube. Observe the colour of the solution. It decolourises in a) B, D b) B, C c) A, C d) C, D Lime water becomes milky on passing CO2 through it due to the formation of: a) Ca (OH)2 b) CaO c) CaCO3. d) None of these The colour of zinc sulphate solution is: a) Red b) Green c) White d) Yellow Universal Tutorials – X CBSE (2012–13) – Chemistry

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42) Zinc metal reacts both with acids and bases to produce hydrogen gas. The nature of zinc metal is: a) Basic b) Neutral c) Acidic d) Amphoteric 43) Zn is added to white coloured solution of aluminum sulphate then after some time the solution: a) Becomes blue b) Remains same (white) c) Becomes colourless d) Becomes silver in colour 44) When conc. HNO3 reacts with a metal the metallic salt is formed along with: a) Water and nitrogen dioxide b) Hydrogen gas and nitrogen dioxide c) Oxygen gas and nitrogen dioxide d) None of these 45) The correct arrangement of the metals (Cu, Fe, Zn, Al) in the reactivity series is a) Al > Fe > Zn > Cu b) Al > Cu > Zn > Fe c) Al > Zn > Fe > Cu d) Al > Cu > Fe > Zn 46) Fe2O3 + 2Al → Al2O3 + 2Fe. The above reaction is an example of a a) Combination reaction b) double displacement reaction c) decomposition reaction d) displacement reaction 47) What happens when dilute hydrochloride acid is added to iron fillings? a) Hydrogen gas and iron chloride are produced b) Chloride gas and iron hydroxide are produced c) No reaction takes place d) Iron salt and water are produced 48) Metallurgy is the process of a) extracting pure metal from its ore b) extracting metal from its ore c) extracting metal from a mineral d) only electro refining of metals 49) A strip of copper was placed in a beaker containing zinc sulphate solution. On observing the strip the next day, it was noticed that a) The copper strip remained as it was b) The copper strip becomes thinner c) The copper strip becomes thicker d) The colour of the strip changed 50) Aluminium does not get readily oxidized in moist air, because a) It is low in metal activity series b) It is high in metal activity series c) It is covered with layer of its own oxide which does not rub off d) It does not react with oxygen 51) Aluminium is used in thermite welding because a) It has a very strong affinity for oxygen b) It is a very light metal c) It is a powerful oxidizing agent d) none of these 52) When Fe is added to blue coloured solution of copper sulphate then after some time the blue coloured solution becomes a) white b) light green c) remains same d) colourless 53) When zinc metal reacts with NaOH solution – a) H2 gas in produced b) OH ions are released c) O2 gas in released d) None of the above 54) Corrosion of iron is also known as a) rusting of iron b) oxidation of iron c) oxidation and hydration of Fe d) All of the above 55) Rust is a) a red brown flaky substance b) mixture of Fe(III) oxide and H2O c) negative corrosion d) all of the above Volume


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56) For rusting a) only oxygen is required b) only moisture is required c) both oxygen and moisture are required d) none of the above 57) Iron rusts because a) It is only exposed to air for a long time b) It is only exposed to water for a long time c) It is exposed to air and water for a long time d) none of the above 58) Anhydrous CaCl2 is used in the experiment for showing rusting of Fe a) To absorb only O2 from the air b) To absorb only moisture from the air and make it dry c) To absorb both moisture and O2 form the air d) all of the above 59) Distilled water is used in the expt. for rusting of iron a) To free water from the oxygen content b) Because only distilled water can be used for the expt. c) To free CO2 from the water d) all of the above 60) Rusting of iron is an a) oxidation reaction b) reduction reaction c) both oxidation reduction reaction d) none of these 61) Rusting of iron can be prevented by a) galvanization b) painting c) greasing d) all of the above 62) A metal highly resistant to corrosion is a) Al b) Au c) Ag d) all of the above 63) Humid air is a) air containing moisture b) air containing O2 c) air containing both O2 and moisture d) all of the above 64) Galvanizing means a) applying a coat of Zn on iron b) applying a coat of Sn on iron c) applying a coat of paint on iron d) all of the above 65) Rate of rusting is enhanced by a) the presence of acids in water b) the presence of bends, dents, scratches cracks or cuts on surface of iron object c) the presence of CO2, SO2 dissolved in water d) all of the above 66) Activity series of metals means a) arrangement of metals in the decreasing order of their reactivity b) arrangement of metal in the increasing order of the reactivity c) arrangement of metals according to their availability d) none of these 67) The correct arrangement of these metals Mg, Zn, Al, Sn, Fe, Au and Pb in order of their reactivity is a) Mg > Al > Zn > Fe > Sn > Pb > Cu b) Zn > Mg > Al > Fe > Sn > Pb > Cu c) Al > Zn > Mg > Fe > Sn > Cu > Pb d) none of these 68) Hydrogen though a non metal is placed in the reactivity series of metals because a) it is a proton acceptor b) it is an electron donor c) it is a proton donor d) none of these 74


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69) To find the reactivity of Al, Zn, Fe and Cu their a) sulphate salts are used b) their carbonate salts are used c) their chloride salts are used d) none of these 70) Which of the following methods is suitable for preventing an iron frying pan from rusting? a) Applying grease b) Applying paint c) Applying a coating of zinc d) All of the above 71) An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be a) calcium b) carbon c) silicon d) iron 72) Food cans are coated with tin and not with zinc because a) zinc is costlier than tin b) zinc has a higher melting point than tin c) zinc is more reactive than tin d) All of the above ANSWERS: Review Questions: CW Very Short Answers: 1 Mark 1) Gold is low in the reactivity series, i.e. it is very less reactive. It’s a noble metal and hence it is found in free state. Al, on the other hand, is high in the reactivity series and hence it occurs as a compound. 2) X is a non–metal. 3) Fe, Ni, Cr 4) Na and Cl 5) Most reactive – K, Least reactive – Au 6) Copper, Zinc 11) Hg, Br 13) Ag and Au Short Answers: 2-3 Marks 32) Naturally occurring common compound forms (ore) of metals are i) Oxide: Haemetite: Fe2O3 ii) Sulphide: Copper Glance (Cu2S) iii) Carbonate: Calamine (ZnCO3) 33) The element is a metal. Because it forms a basic oxide (turns red litmus blue) and it dissolves in HCl. eg., Sodium is a metal Sodium reacts with oxygen to give sodium oxide, which is a basic oxide. 4Na + O2 → 2Na2O Sodium oxide (basic oxide)

Also, Na dissolves in HCl, 2Na + 2HCl → 2NaCl + H2 Review Questions: HW Objective type questions: 1 Mark 1) three 2) seven 3) active 4) neutral 5) mineral 6) density 7) carats 8) False 9) False 16) a 18) Aluminium 19) Due to their tendency to release electrons and thus become positively charged. 20) Valency = +2, reducing properties (Since, it will lose two electrons readily and reduces the species with which it comes across. 86) Metals, depending upon their reactivity, react with dilute acids at different rates. More reactive metals react vigorously and the less reactive ones react slowly or do not react. When Na, Mg and Cu are reacted with dil. HCl: (i) Na reacts vigorously, Mg reacts quite rapidly but less vigorously than Na and Cu does not react. Mg + 2HCl → MgCl2 + H2 Cu + HCl → No reaction 2Na + 2HCl → 2NaCl + H2 ii) H2 is given off when Na reacts with HCl it catches fire instantly however this is not the same with of H2 liberated when Mg reacts with HCl. Hence these activities show that reactivity of the above given metals is in the following order: Na > Mg > Zn 105) B > A > C Volume


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NCERT Exercises: 1) (i) Hg (ii) Sodium (iii) Silver (iv) Lead 3) Na is so reactive that it catches fire at room temperature. It reacts vigorously with moisture of air, so to protect it; Na is kept under kerosene. 4) i) Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g) ii) Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g) 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g) 5) i) B ii) Displacement reaction takes place iii) B, A, C, D 6) H2 gas is liberated, Fe + H2SO4 → FeSO4 + H2↑ 7) Zinc displaces Fe from FeSO4 forming ZnSO4. Zn + FeSO4 → ZnSO4 + Fe Na x •• × x 8) i) N a ; • O • , Mg xx ii) a) O = Na2O b) Mg x + O = MgO •• Na x iii) Cations and Anions Mg xx 9) Considerable amount of energy is required to break the strong inter–ionic attraction, as ionic bonds are polar and are very strong. 11) Ag, Au 12) Reduction ; Heating 13) Metal Zinc Magnesium Copper Zinc oxide No reaction Displacement No reaction Magnesium oxide No reaction No reaction No reaction Copper oxide Reaction Reaction No reaction 14) Noble metals 19) Galvanising, painting 20) Acidic oxide 21) a) They do not corrode, they have shinning surface and they have a very good look about them. c) It corrodes to form Al2O3 which is a protective layer for the Al metal lying underneath. Hence, no corrosion of the metal takes place even when food is cooked/stored in them d) As oxides can be easily reduced to obtain respective metals. 22) Tarnished Cu is a layer of CuCO3 on Cu, CuCO3 + acid → CuO (shinning) + CO2↑ 24) Aqua regia, which is a mixture of 3:1 HCl and HNO3 respectively. This mixture dissolved Gold. 25) Copper does not react with water at all. While steel (alloy of Fe) reacts with hot water to give Fe3O4. Chemical equation: 3Fe(s) + 4H2O → Fe3O4(s) + 4H2(g) 26) 2 metals that will displace H2 from dil acids are Zn, Na. 2 metals that will not displace H2 from HCl are Cu, Sn. 27) Anode is a thick rod of the impure metal and Cathode is a pure metal (thin sheet) electrolyte is the salt of the metal that is to be refined. Note: Not all questions have been solved from the miscellaneous exercise behind the chapter. Students are expected to answer these questions on their own on completion of the chapter.

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Chapter 06: Life processes

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Chapter 06: Life Processes Chapter Map: Nutrition Modes of Nutrition Autotrophic

Heterotrophic

Photosynthesis

Saprophytic

Factors affecting Photosynthesis (Activities) Nutrition in Animals Amoeba

Parasitic Holozoic

Humans

Respiration Types of Respiration Aerobic

Anaerobic

Diffusion Respiration in Plants and Animals Respiratory System of Man Transportation Internal Structure of Heart Exchange of Gases Blood Vessels Blood Platelets Lymph Transportation in Plants Transport of Water

Transport of Food and Other Substances

Excretion Excretion in Human Beings

Excretion in Plants

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Life Processes:  Movement of various types can be taken as indication of life.

Definition: 

Life processes can be defined as the processes which together perform various functions of the body.

Criteria to identify living organisms:   

Breathing, Respiration, movement of animals. Growth of the plants. Molecular movements as seen in cells of the body of animals and plants

Importance of Life Processes: 

The maintenance of life requires processes like nutrition, respiration, transport of materials within the body and excretion of waste products

Nutrition:  

For every individual to grow nutrient is must which is completed by nutrition. Nutrition is the intake and utilization of substances that are necessary for growth, energy, maintenance and activities of the plants or animals.

Respiration: 

Simple molecules obtained after digestion need to be broken down by chemical reactions like oxidation and reduction.  Breakdown of this molecules release tremendous amount of energy required to carry out various function in our body.  Respiration can be defined as biochemical process which involves the intake of oxygen from outside the body and use it in the process of break down of food sources for cellular needs.

Transportation: 

Whatever food and oxygen is taken by the organism has to be transported to all the parts of the body. Thus this is possible by the process of transportation, with the help of circulatory system.

Excretion: 

The metabolic activities going in our body creates many byproducts or waste products (nitrogenous waste) which has to be eliminated from the body otherwise it may turn into toxic and be harmful to body.  So the process of excretion is necessary for removal of waste products from the body. It is carried out by the excretory system.

Diffusion: 

Simple diffusion can be seen in unicellular organisms where the body is in direct contact with the environment. They do not need special organs for intake of food, exchange of gases or removal of wastes.  In multicellular organisms the body is not in direct contact with the environment so simple diffusion is not possible and cannot meet the oxygen requirements of all the cells.

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Nutrition:  Nutrition is defined as the procurement and utilization of substances that are necessary for growth, energy, maintenance and activities of the plant or animals or in other words, it is the process of intake, as well as utilization of nutrients by an organism.  The chemical substances that provide nourishment (as energy source or for biosynthesis of body constituents) to living organisms are called nutrients.  Nutrients may be:  Simple organic molecules  Complex organic molecules  Inorganic or mineral ions

Modes of Nutrition:  Basically, there are two modes of nutrition i.e. autotrophic and heterotrophic nutrition Nutrition

Autotrophic

Heterotrophic

Phototrophic (Eg. Plants)

Saprophytic (e.g. yeast, moulds, mushrooms)

Chemotrophic (Eg. Bacteria)

Parasitic (e.g. cuscuta, tape worms, orchids, lice, round worms, leeches and ticks) Holozoic (e.g. amoeba, frog, human being)

Autotrophic Nutrition:      

The process mainly occurs in green plants and some forms of bacteria. The mode of nutrition in which an organism builds up its own organic food from inorganic substances is known as autotrophic nutrition. The organisms showing autotrophic nutrition are called autotrophs. The autotrophs synthesise their food either by the process of photosynthesis or by chemosynthesis. Carbohydrates are utilised for providing energy to the plants. In plants the carbohydrates which are not used are stored in form of starch which serves as the internal energy reserve. In human body the energy derived from the food is stored in the form of glycogen.

Photosynthesis:      

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Plants prepare food in the form of carbohydrates and proteins by the process of photosynthesis. Photosynthesis literally means, “to put together by light”. Photosynthesis means synthesis of organic matter by the autotrophs (phototrophs) in the presence of light, using chlorophyll, CO2 and H2O. Photosynthesis is the only process by which the solar energy is trapped by the producers and converted to food energy for all the organisms. It is the only natural process in which CO2 is consumed and oxygen is liberated. The overall equation of photosynthesis is, Universal Tutorials – X CBSE (2012–13) – Biology

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80 sunlight 6CO2 + 6H2O  → C6H12O6(glucose) + 6O2 chlorophyll

sunlight OR 6CO2 + 12H2O  → C6H12O6(glucose) + 6H2O + 6O2 chlorophyll

Events occurring during Photosynthesis: 

Absorption of light energy by chlorophyll.  Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen (light reaction and photolysis of water).  Reduction of CO2 to carbohydrates (Dark reaction or Calvin Cycle).  All the above events do not occur in sequence for e g. In desert plants they take up CO2 at night and prepare an intermediate which is acted upon by the energy absorbed by the chlorophyll during the day. Chloroplast – The Site of Photosynthesis:   

Plant cells have chloroplast, (an organelle) which contain chlorophyll. The green colour of the plants is due to presence of pigment chlorophyll. Chlorophyll is a photosynthetic pigment.

Raw Materials During Photosynthesis: 1)

Carbon dioxide and Water:  The synthesis of carbohydrates requires two substances i.e. carbon dioxide and water.  The plants use carbon dioxide, which is present in atmosphere and is released during respiration. It enters into the plant leaf through specialized pores called stomata.  The aquatic plants use carbon dioxide dissolved in water.  Water required for photosynthesis is absorbed by roots from the soil through osmosis.  Water moves up through the xylem to the leaves and ultimately to photosynthesizing cells. Other materials:  It includes nitrogen, phosphorus, iron and magnesium.  Nitrogen is used for photosynthesis of proteins and other compounds.  This is taken up in the form of inorganic nitrates and nitrites.  It is also taken up in the form of organic compounds prepared by bacteria from atmospheric nitrogen.

2)

Factors Affecting Photosynthesis: 

The various factors influencing the rate of photosynthesis (and hence productivity) are as follows:

Light Intensity: 



In the absence of light of sufficient intensity, the plants do not photosynthesize. Instead, they take in oxygen and release carbon dioxide i.e. they respire. The rate of photosynthesis increases at the lower intensities of light and decreases at higher intensities.

Availability of Carbondioxide: 

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The rate of photosynthesis increases with increase in CO2 content. But after a certain limit, there is no effect of CO2 concentration on photosynthesis and further increase can be inhibitory. Universal Tutorials – X CBSE (2012–13) – Biology

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CO2 is a limiting factor in photosynthesis on clear summer days when plants are provided with adequate water. In land plants, the CO2 enters the leaf through stomata. Hence when the stomata are closed, rate of photosynthesis is zero.

Stomata:     

Exchange of gases occurs across the surface of stems, roots and leaves by specialize structures called as stomata. Stomata are small pores present on upper (monocots) and lower (dicots) surface of leaf. The opening and closing of the pore is a function of the guard cells. Guard cells swell when water enters inside and stomatal pore opens. When the guard cells shrink the pore closes. [This space is left intentional for student to draw diagram]

(a)

(b)

(a) Open and (b) closed stomatal pore

Heterotrophic Nutrition: 

The mode of nutrition in which the organisms obtain water, minerals or certain organic compounds from other organisms, i.e. the autotrophs, is known as heterotrophic nutrition.  Mostly animals, bacteria and fungi show heterotrophic nutrition. The organisms showing heterotrophic nutrition are called heterotrophs.  In this mode of nutrition, complex molecules are digested into simpler forms, which are then utilized by organisms.  Heterotrophic nutrition is of different types i.e. saprophytic, parasitic and holozoic nutrition. Saprophytic (Saprozoic) Nutrition: 

In this mode of nutrition, organisms grow and live on dead or decaying organic matter including animal and plant remains. They break down the food material outside the body and then absorb it.

Parasitic Nutrition: 

In this mode of nutrition, the organism (parasite) depends upon other organism (host) for its nutritional requirements. They derive nutrition from plants or animals without killing them.

Holozoic Nutrition: 

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All vertebrates and many invertebrates eat whole plants, whole animals or their parts. So mode of nutrition in which complex organic matter from plants or animals is ingested, digested and absorbed is called holozoic nutrition.


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Nutrition in Animals:    

In unicellular organisms the food is taken in by the entire surface. Eg. Paramoecium has a definite shape and food is taken in at a specific spot. Food is moved to this spot by the movement of cilia which cover the entire surface of the cell. In multicellular organisms they have specific system called as digestive system to perform the process of nutrition / digestion.

Nutrition in Amoeba:  The food of Amoeba consists of planktonic (that float on water body) microscopic plants and animals.  Its mode of nutrition is holozoic.  Amoeba obtains its food by a process called phagocytosis.  Amoeba engulfs the food with the help of pseudopodia.  When the food is completely encircled, tips of pseudopodia touch each other. The membrane at that point dissolves and the food is stored in food vacuole.  Amoeba shows intracellular digestion.  Lysosomes containing digestive enzymes fuse with the food vacuole to form the digestive vacuole.  The enzymes break the larger molecules into smaller molecules (digestion).  The membrane of the vacuoles is drawn into fine canals, which transfer the products of digestion into the cytoplasm (absorption).  In the cytoplasm, the food is utilized by the cell (assimilation)  The undigested matter is thrown out of the cell by exocytosis (egestion).

Human digestive system:  Alimentary canal is 9 m long extending from mouth to anus.

Mouth: 

Mouth is the front opening of alimentary canal bounded by two sensitive lips. Mouth opens into buccal cavity.

Buccal Cavity 

Buccal cavity is provided with 4 types of teeth for cutting, tearing, chewing and grinding the food.  Muscular tongue is present at the floor of buccal cavity which bears taste buds and acts as a sense organ for taste.  Tongue helps in pushing the food to pharynx.

Salivary Glands: 

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When the food is taken in the mouth it is made soft by Saliva secreted by salivary glands in the mouth. Saliva contains an enzyme called salivary amylase which converts starch into sugar. Thus digestion starts in buccal cavity


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Human alimentary canal

Oesophagus: 

The food crushed in the mouth is taken to the stomach by long muscular tube called oesophagus.  This is also called as gut which pushes the food to stomach by peristaltic movement. No digestion takes place here.

Stomach: 

It is a large J–shaped organ present on the left side of the abdomen. The stomach wall has branched and tubular glands called gastric glands.

Gastric Glands: 

They secrete gastric juice. Gastric juice is a mixture of three secretory products like HCl, Protein digesting enzyme (Pepsin) and mucus.

Functions: 



  



Muscular walls of the stomach help in mixing the food thoroughly with more digestive juices (Churning of food). Hydrochloric acid creates an acidic medium which facilitates the action of the enzyme pepsin. HCl also kills the bacteria and makes the food disinfectant. Pepsin breaks down proteins into peptones. Mucus protects the inner lining of the stomach from the action of the acid under normal conditions. Thus, when food reaches stomach it mixes with gastric juice and protein digestion starts in the stomach.

Small intestine: 

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Food from the stomach enters into small intestine regulated by sphincter muscles. Small intestine is the longest part which is fitted into compact space because of the coiling.


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

  

Complete digestion of fats, carbohydrates and proteins takes place in small intestine. Food coming from stomach to small intestine is acidic. This food is made alkaline with the help of secretions of liver and pancreas, so that it is easy for the action of pancreatic enzymes. The secretion of liver and pancreas are poured in duodenum part of intestine.  Liver: It is present on the right side of the abdomen. Liver secretes bile which contains bile pigment and bile salts. Bile salt breaks the larger fat molecules into small globules and increases the efficiency of enzyme action (Emulsification of fats).  Pancreas: It is a large gland lying parallel to and beneath the stomach. It secretes digestive enzymes as well as the hormones (insulin and glucagon). Pancreas secretes pancreatic juice which contains enzymes like trypsin and lipase. Trypsin digests proteins and Lipase helps in breaking down of emulsified fats. Walls of small intestine also contain glands which releases intestinal enzymes for the complete digestion of food. Final conversion done by Enzymes:  Proteins are converted to amino acids.  Carbohydrates are converted to glucose.  Fats are converted to fatty acids and glycerol.

Summary of digestion Starch (Complex Sugar) Proteins

Lipids (Large molecules) Emulsified fats

Salivary amylase / Ptyalin

Pepsin acidic medium Bile salts

P. lipase alkaline medium

Simple sugar

Peptones

Emulsified fats (Small fat globules) fatty acids + glycerol

Starch (Complex Sugar)

P. amylase alkaline medium

Simple sugar

Peptones

P. trypsin alkaline medium

Peptides

Absorption of Small intestine: 

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Internally the walls of small intestine are provided by long finger like projections called as villi. Whose functions is i) Increasing the surface area for absorption. ii) Carry the absorbed food to each and every cell of the body as they are rich in blood vessels. iii) The absorbed food in the form of simple molecules reaches the cells through blood stream and is utilized. Utilization of food means using it for building up new tissues, repair of old tissues and for obtaining energy.


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Large intestine: 

The unabsorbed food is sent to large intestine where more villi absorb water from this material.

Rectum: 

The undigested food collects as faecal matter in the rectum.

Anus: 

The waste material is thrown out from the body by anus regulated by anal sphincter.

Note: Length of small intestine is different in various animals depending on the food they eat. Herbivores have longer small intestine because they eat grass and the cellulose has to be digested. Carnivores have shorter small intestine because they eat meat which is digested easily. APPENDIX:

Activity 6.1 : Aim: Chlorophyll is necessary for photosynthesis Steps

Reasons / Observation

Take a potted plant with variegated leaves eg. Crotons Keep it in dark room for 3 days

To remove the starch

Keep the plant in sunlight for about 6 hrs. Pluck a leaf and mark green area in it and trace them on sheet of paper. Dip the leaf in boiling water for few minutes

To remove chlorophyll

Place the leaf in boiling alcohol. What is the colour of solution?

To decolorize the leaf. Colour of the solution will be green

Dip the leaf in iodine solution for few minutes

To mark the areas of starch

Remove the leaf and rinse off the iodine solution Observe the colour of the leaf and compare with tracing of the leaf done in the beginning

Portion of leaf having chlorophyll turns blue − black while non –green parts do not turn blue – black. In the earlier leaf it was colourless

Conclusion / Inference: 



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Starch formation takes place in that part of the leaf which has chlorophyll. Starch is not formed in the absence of chlorophyll. Chlorophyll is necessary for photosynthesis.


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Activity 6.2: Aim: CO2 is necessary for photosynthesis

Bell jar Watch glass containing potassium hydroxide

(a) (b) Experimental set-up (a) with potassium hydroxide (b) without potassium hydroxide

Steps

Observation / Reasons

Take two healthy potted plants of same size Keep in dark room for 3 days

To remove the starch from leaves

Place each plant on separate glass plates. Place a watch – glass containing potassium hydroxide by the side of one of the plants.

Potassium hydroxide carbondioxide

is

used

to

absorb

Cover both the plants with separate bell jars Vaseline should be used to seal the bottom of the jars to the glass plates.

To keep the set – up airtight

Keep the plants in sunlight for 2 hours Pluck a leaf and check for presence of starch.

Starch will be seen in bell jar ‘b’

Do both the leaves show the presence of the same amount of starch?

No,

Conclusion: 

Photosynthesis will occur in the presence of carbondioxide in bell jar ‘b’ and not in ‘a’. So carbondioxide is necessary for photosynthesis.

Activity 6.3: Aim: To check the action of saliva on starch Steps Take 1 mL starch solution (1%) in two test tubes (A and B). Add 1 mL saliva to test tube A and leave both test tubes undisturbed for 20-30 minutes. Now add a few drops of dilute iodine solution to the test tubes. In which test tube do you observe a colour change? What does this indicate about the presence or absence of starch in the two test tubes? What does this tell us about the action of saliva on starch?

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To detect the broken down starch In test tube A Starch is broken down in test tube A and undigested in test tube B The saliva contains an enzyme called salivary amylase that breaks down starch which is a complex molecule to give sugar.


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Respiration:  Organisms require energy to maintain various life processes.  The energy needed is obtained from the oxidation of simple organic compounds like glucose and for this a continuous supply of oxygen is needed.  Respiration is a biochemical process taking place in the mitochondria with the help of several enzymes.  The energy released in respiration is chemical energy which gets stored in adenosine triphosphate molecules (ATP).

Types of Respiration:  Depending upon the requirement of oxygen, the respiration is of two types i.e. aerobic and anaerobic respiration.  The first step is the break-down of glucose, (a six-carbon molecule) into a three-carbon molecule called pyruvate.  This process takes place in the cytoplasm, which is independent of oxygen. Further, the pyruvate may enter into aerobic and anaerobic respiration. Absence of oxygen (in yeast) In cytoplasm

Glucose

Pyruvate (3–carbon molecule)

(6–carbon molecule)

+ Energy

Lack of oxygen (in our muscle cells) Presence of oxygen (in mitochondria)

Ethanol + Carbon dioxide + Energy (2–carbon molecule)

Lactic acid + Energy (3–carbon molecule)

Carbon dioxide + Energy

Break–down of glucose by various pathways Aerobic Respiration:  







It takes place in the presence of oxygen and food is oxidized completely. It breaks down 3 carbon pyruvate molecules to give 3 molecules of CO2. Other product is H2O Breakdown of pyruvate using oxygen takes place in the mitochondria with release of high energy. It produces 38 ATP per molecule of glucose, e.g., body tissues of vertebrates. The highenergy bonds of ATP are subsequently broken down to use the energy for various activities. It is commonly seen among higher plants and animals.

Anaerobic Respiration:  







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Respiration occurring in the absence of O2 is called anaerobic respiration. Since this process takes place in the absence of air (oxygen), it is called anaerobic respiration. In one type of anaerobic respiration known as alcoholic fermentation, CO2 and ethanol are formed as byproducts. This process takes place in yeast during fermentation In other type of anaerobic respiration known as lactic acid fermentation, the end product is lactic acid. This process takes place in lactic acid bacteria, skeletal muscles. Comparatively less energy is released. It produces 2 ATP per molecule of glucose. For example- Yeast, lactic acid bacteria, intestinal parasites, liver flukes, skeletal muscles (during exercise) and erythrocytes. Universal Tutorials – X CBSE (2012–13) – Biology

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Respiration in Plants:  Respiration in plants involves the exchange of oxygen and carbon dioxide (respiratory gases).  Respiration in plants differs from that in animals in following respects:  Root, stem and leaves perform respiration individually.  There is little transport of gases from one part to another.  Respiration occurs at a slower rate as compared to animals.  Roots take up oxygen present in between the soil particles by the process of diffusion.  Diffusion is the movement of substances from a region of high concentration to a region of low concentration.  Oxygen diffuses into the root hairs and passes into other cells of the root.  Carbon dioxide from the root cells similarly moves out into the soil.  The direction of diffusion depends upon the environmental conditions and the requirements of the plant.  At night, when there is no photosynthesis occurring, CO2 elimination is the major exchange activity going on.  During the day, CO2 generated during respiration is used up for photosynthesis; hence there is no CO2 release. Instead, oxygen release is the major event at this time.

Respiration in Animals:  Animals are provided with certain specialized structures called respiratory organs through which exchange of gases takes place.  Respiratory organs may be skin (earthworm), gills (fish), trachea (insect) or lungs (human).  Characteristic features of respiratory organs are:  A large surface area to get enough oxygen.  Thin walls for easy diffusion and exchange of respiratory gases.  They should be richly supplied with the blood.  Air may reach cells of the body directly (as in trachea) or indirectly (as in skin, lungs and gills).

Aquatic animals:  Most of the aquatic organisms used gills as their respiratory organs eg. prawns, fish and tadpoles  The exchange of gases in the gills is known as branchial respiration.



Why rate of breathing in aquatic organism is much faster than that seen in terrestrial organisms? Ans: Since the amount of dissolved oxygen is fairly low compared to the amount of O2 in the air.

Terrestrial animals:  Respiration is carried out with the help of lungs as the chief organ in terrestrial vertebrates.  Terrestrial vertebrates use the oxygen present in air with the help of lungs eg. reptiles, birds and mammals.

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Human Respiratory System:  Human respiratory system consists of external nares, pharynx, larynx, trachea, bronchi, bronchioles and lungs. [This space is left intentional for student to draw diagram]

Human respiratory system

External Nares or Nostrils: 

These are present at base of tip of nose. These are the structures through which the air is drawn in and is filtered by fine hairs that line the passage.  Here the air is warmed, moistened and freed from dust particles which are entrapped in the mucous secretions of glands inside nasal cavity. 

Throat: 

Air passes through throat and into the lungs.  Rings of cartilage are present in the throat which ensures that the air passage does not collapse

Lungs:  

  

Lungs are a pair of hollow, elastic, conical bag-like organs. They are situated in the thoracic cage formed by a part of the vertebral column on the dorsal side, sternum (breast bone) on the ventral side and a series of curved bony ribs laterally. The ribs are connected with the vertebral column and sternum. Within the lungs the throat divides into two divisions left and right bronchi. These further divides into small tubes called as bronchioles. The bronchiole terminates into thin walled balloon like structure called as air sacs or alveoli. A thin, highly permeable membranous wall surrounded by many blood capillaries lines each alveolus.

Exchange of gases at lungs:  



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Branches of pulmonary artery supply blood to alveolar capillaries. The blood brings CO2 from rest of the body to alveoli and the O2 in the alveolar air is taken up by blood in the alveolar blood vessels to be transported to all the cells in the body. The oxygenated blood is then returned from alveolar capillaries to pulmonary veins. Universal Tutorials – X CBSE (2012–13) – Biology

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Note: There are about 300 million alveoli in a man’s lungs offering a surface area of 400-800 square feet.

Mechanism of Breathing:  Breathing consists of two phases: inhalation and exhalation.

Inhalation: 

When we breathe in, the air from outside rushes into the alveoli of the lungs.  During this process, the diaphragm is pulled outwards, thereby increasing the volume inside the thoracic cavity, as the intercostal and the diaphragm muscles contract.  The pressure decreases due to which the air rushes in.

Exhalation: 

Carbon dioxide is pushed out through the lungs as the diaphragm muscles relaxes and comes back to its normal position, due to which the pressure increases inside the thoracic cavity and the air moves out.

Breathing Cycle: 

It is a physical process which involves inspiration of fresh air and expiration of foul air Rate of breathing under normal condition is 15–18 times per min.  In 1 min. we breathe in about 500 ml of air 

Residual Volume of Air: 

This is the amount of air left in lungs which cannot be expelled even after forceful expiration.  Since residual vol. of air is present in lungs there is sufficient time for O2 to be absorbed and for the CO2 to be released.

Exchange of Gases in Tissues:     

When the air is breathed in, it ultimately reaches the alveoli. Alveoli surface being thin, diffusion of gases takes place. Hence, O2 enters the blood and ultimately reaches the tissues. In tissues, exchange of gases again takes place. Haemoglobin present in RBC has affinity towards O2. So they take up oxygen from air in the lungs and carry it to tissues which are deficient in O2  Oxygen enters the cells and is utilized for oxidation of food for release of energy.  Carbondioxide from tissues enter blood, get exchanged at alveoli and is thrown out during exhalation.  CO2 is easily soluble in water than O2. So CO2 is transported in dissolved form in our blood.

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APPENDIX:

Activity 6.4: Aim: To check amount of CO2 in the air that we exhale.

(a) Air being passed into lime water with a pichkari / syringe, (b) air being exhaled into lime water

Steps Take some freshly prepared lime water in a test tube. Blow air through this lime water. Note how long it takes for the lime water to turn milky. Use a syringe or pichkari to pass air through some fresh lime water taken in another test tube Note how long it takes for this lime water to turn milky. What does this tell us about the amount of carbon dioxide in the air that we breathe out?


Lime water turns milky It will take less time

It will take more time Expired air contains more carbondioxide as compared to CO2 content in atmospheric air

Activity 6.5: Aim: Respiration occurring in absence of oxygen. Steps Take some fruit juice or sugar solution and add some yeast to this. Take this mixture in a test tube fitted with a one-holed cork. Fit the cork with a bent glass tube. Dip the free end of the glass tube into a test tube containing freshly prepared lime water. What change is observed in the lime water and how long does it take for this change to occur? What does this tell us about the products of fermentation?


Condition inside the test tube is anaerobic respiration i.e., fermentation which take place only in the presence of easily available carbohydrates and in absence of oxygen Incomplete oxidation of carbohydrates take place. CO2 turns lime water milky and it will take longer time since CO2 is produced at the end of fermentation. Ethanol and CO2

Conclusion: 

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Fermentation is incomplete oxidation occurring in absence of free O2


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Activity 6.6: Aim: To check the breathing rate of fish and human Steps


Observe fish in an aquarium. They open and close their mouths and the gill-slits (or the operculum which covers the gill-slits) behind their eyes also open and close. Are the timings of the opening and closing of the mouth and gill-slits coordinated in some manner?

Yes, first the mouth will open and close. When the mouth closes the gill–slits will open and close. In this way a co–ordination between mouth and gill–slits is seen.

Count the number of times the fish opens and closes its mouth in a minute.

Do it yourself

Compare this to the number of times you breathe in and out in a minute.

15–18 times per minute

Transportation: Transportation in Humans:  There is need to transport various substances like digested food materials (to provide energy and growth of the body) hormones, metabolic wastes, enzymes and various gases like oxygen and carbon dioxide to the respective organs & tissues.  In humans, the transport of substances is done by a system called the circulatory system.  Circulatory system has three main components i.e. blood (circulatory fluid), blood vessels (arteries, veins and capillaries) and heart.  Blood flows in blood vessels, which divide and redivide and ultimately reach each and every part of the body.  Heart is an organ which pumps and receives blood.  Thus circulatory system performs the following functions in the human body.  Transport of nutrients.  Transport of excretory products.  Transport of respiratory gases.  Transport of metabolic intermediates.  Transport of hormones.  Body temperature regulation.  Maintenance of pH.(buffer system).  Protection from diseases.

Blood Composition: 

Blood is a red-coloured connective tissue fluid that circulates in the body through a system of vessels due to the pumping action of the heart.  Blood accounts for 30-35% of the total extracellular fluid present in the body.  Blood is compose of three types of blood cells and plasma. RBCs / Erythrocytes: 

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RBCs contain respiratory pigment haemoglobin which carries O2 to the tissues. Universal Tutorials – X CBSE (2012–13) – Biology

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WBCs / Leucocytes: 

WBCs acts as soldier and protect the body from infections.

Platelets / Thrombocytes: 

 

Blood platelets (thrombocytes) are enucleated, round or oval, biconvex, disc like bodies, found in mammalian blood. They are fragments of cells. Blood platelets help in clotting of blood.

Plasma: 

It transports food, carbondioxide and nitrogenous wastes in dissolved form.

Note: Blood does not clot in blood vessels due to the presence of heparin secreted by mast cells and antithrombin.

Structure and Function of Heart and Blood Vessels: Human Heart:       

Heart is a reddish brown, hollow muscular organ made up of cardiac muscle fibres. Heart is the muscular pumping organ of the blood vascular system. Heart beats about 70-80 times per minute. The human heart lies between the lungs in the middle of the thoracic cavity, inclined to the left. The heart is enclosed in a tough, double walled membrane, the pericardium. The heart consists of four chambers, two atria and two ventricles. The right and left halves are completely separated by muscular partition called septa. The right side of the heart deals with deoxygenated blood while the left side deals with oxygenated blood. [This space is left intentional for student to draw diagram]

Internal structure of the human heart 

Atrium receives blood from large veins. There are valves between left auricle and left ventricle (bicuspid or mitral valve) and right atrium and right ventricle (tricuspid valve).  These valves permit the flow of blood from atria to ventricles but not in other direction.  Right atrium receives the deoxygenated blood from the body through superior vena cava, inferior vena cava and coronary vein. 

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94 

     

Superior vena cava drains blood from the upper part of body, inferior vena cava drains blood from middle and lower part of the body whereas coronary vein drains blood from the heart itself. Left auricle receives the oxygenated blood from the lungs through pulmonary veins. Right ventricle pours the blood into pulmonary arteries which reach lungs. Left ventricle distributes the oxygenated blood to all the parts of body through the largest artery called aorta. Right wall of right atrium bears a specialized bundle of muscles called sinoatrial node (SA node). SA node is called the pacemaker of heart because it functions as originator of cardiac impulse and heart beat. There is one more specialized muscle bundle called atrioventricular node (AV node). It helps in the conduction of cardiac impulse.

Working of Heart: 







  





Beating of heart is due to rhythmic contraction and relaxation of heart muscles. When the muscles of all the four chambers are relaxed, the vena cava pour deoxygenated blood into right atrium and pulmonary veins pour oxygenated blood into left atrium. When the atria are filled with blood, they contract. During atrial contraction, right atrium pours blood into right ventricle and left atrium pours blood into left ventricle. Schematic representation of transport and exchange of Now the ventricles contract draining the oxygen and carbon dioxide blood into pulmonary artery (from right ventricle) and aorta (from left ventricle). So in this way, deoxygenated blood comes to the heart, goes to lungs for oxygenation and again comes back for distribution. Since, the blood flows twice through the heart, it is called double circulation. Single circulation: Fishes, on the other hand, have only two chambers to their hearts, and the blood is pumped to the gills, is oxygenated there, and passes directly to the rest of the body. Thus, blood goes only once through the heart in the fish during one cycle of passage through the body.

Why ventricles have thick muscular walls?

Ans: Because they have to pump blood into various parts of the body than the atria do.



How does the separation of right side and left side of the heart useful?

Ans: It keeps oxygenated and deoxygenated blood from mixing. Such separation allows a high efficient supply of oxygen to the body.

Blood Vessels:  Blood vessels are of three kinds: arteries, veins and capillaries.

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Arteries: 

Arteries are the elastic thick walled blood vessels, which carry the blood away from the heart to various organs of the body.  They are thick because blood emerges from heart under high pressure.  All the arteries carry oxygenated blood except pulmonary artery.  Largest arteries like pulmonary artery and aorta are provided internally with semilunar valves to prevent backward flow of blood.

Veins: 

Veins are the thin walled blood vessels with valves which collect blood from different organs of the body and carry them to the heart. They are thin walled because the blood is no longer under pressure.  All the veins carry deoxygenated blood except pulmonary vein.  They have valves that ensure that the blood flows in one direction

Capillaries: 

Capillaries are thin walled extremely narrow microscopic blood vessels forming a network in the tissues or organs.  They occur at the terminals of arteries and veins and they connect both arteries and veins.  Exchange of food material, gases and waste takes place through capillaries.

Lymphatic System:  It is network of small vessels that resembles blood vessels. The lymphatic system returns fluid from body tissue to the blood stream. The lymphatic system is an open system consisting of lymph vessels, lymph nodes and lymph sinuses.  Lymph is a colourless or slightly yellowish viscous fluid, which is derived from tissue fluid and is present inside special tubes called lymph vessels.  It is also called extra cellular fluid as it bathes the cells and lies outside them.  Lymph does not possess erythrocyte and blood platelets.  Lymph flows unidirectional i.e. from tissues to heart.  The movement of lymph is due to the squeezing action of the surrounding muscles. Lymph

Capillary Vein

Artery

Veinule

Arteriole

Lymphatic system Note: Diagram is for reference only

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Function of lymph: 

Lymph contains lymphocyte cells; it helps in fighting against infections.  Lymph carries digested and absorbed fat from intestine and drain excess fluid from extracellular space back into the blood  It acts as a middleman as it returns proteins and fluid from circulation to tissues.

Transportation in Plants: Raw Materials and Source:  Main source is Soil.  Raw materials: nitrogen, phosphorus and other minerals.  Main part of plant for absorption of minerals and water are roots.

Condition for Easy Diffusion: 

The distance between soil–contacting organs & chlorophyll containing organ should be small  So that energy raw materials can easily diffuse to all parts of the plant body.  If distances are large diffusion processes will not be sufficient to provide raw material in leaves and energy in roots.

Plant Transport System:    

   

In leaves, water and CO2 are used for photosynthesis. Plants having low energy needs will use slow transport system. In tall trees the energy needs will be more so it will use fast transport system. Two pathways include conducting tubes like  Xylem: moves water and minerals obtained from the soil.  Phloem: transports products of photosynthesis from the leaves to other parts of the plant. Water is essential for normal growth and development of plants. Water gives turgidity to the plants. Turgidity is necessary for non-woody tissues for mechanical support. Loss of turgidity leads to wilting of leaves and dropping of shoots. The plants absorb water and minerals mainly through roots and transport them to various parts of the plant like stem, leaves and flowers.

Absorption of Water by Plants:      

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Water can enter plants through its entire surface but maximum water is absorbed through the roots, especially at the tips. The root hairs increase the surface area for absorption of water. The water enters the root hairs and from there it reaches the epidermis, root cortex, endodermis and reach the xylem vessels through which it is further transferred. Water and minerals dissolved in it moves up through the conducting tissue called the xylem, which is made up of tracheids and vessels. In Xylem tissues, vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water conducting channels reaching all parts of the plants. The cells of the roots in contact with the soil actively take up ions, which creates the difference in the concentration of these ions between the root and the soil. Universal Tutorials – X CBSE (2012–13) – Biology

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Water continuously moves into the root cells to eliminate the difference and creates a column of water which is steadily pushed upwards.  However, this pressure by itself is unlikely to be enough to move water over the heights so they use another strategy to move water in the xylem upwards to the highest points of the plant body (Transpiration)

Transpiration:      

The loss of water in the vapour form from the leaf into the atmosphere through the stomata present along the lower surface of leaf is called transpiration. Evaporation of water molecules from cells of a leaf creates a suction which pulls water from xylem cells. This is known as transpirational pull. Thus, transpiration is a necessary evil as it is necessary for the upward movement of sap (ascent of sap) from roots to leaves. Magnitude of transpiration is sufficient to raise the water upto top of tallest trees. Under optimal conditions, leaf can transpire its own weight of water in less than an hour. A tree transpires water equivalent to 100 times its weight in its lifetime.

Functions: 





Transpiration helps in the absorption and upward movement of water and minerals dissolved in it from roots to the leaves. It also helps in temperature regulation. The effect of root pressure in transport of water is more important at night. During the day when the stomata are open, the transpiration pull becomes the major driving force in the movement of water in the xylem.

Transportation of Food and other Substances:  The food material synthesized in the leaves and hormones synthesized at the shoot & root tip are generally translocated downwards or upwards through the phloem.  Phloem transports amino acids other substances to the storage organs of roots, fruits and seeds.  Phloem is made up of sieve tube and companion cells.  The most commonly translocated carbohydrate in the plant is sucrose.  The food is synthesized in mesophyll cells of the leaves. From the mesophyll cells, food molecules enter the phloem elements or cells.  Moreover, the hormones synthesized at the shoot and root tips are transported to other parts of plants through phloem.  In the phloem, food can move upwards or downwards to all parts of the plants by utilizing energy from ATP. Note: Exact procedure: Material like sucrose is transferred into phloem tissue using energy from ATP. This increases the osmotic pressure of the tissue causing water to move into it.  This pressure moves the material in the phloem to tissues which have less pressure.  This allows the phloem to move material according to the plant’s needs. For example, in the spring, sugar stored in root or stem tissue would be transported to the buds which need energy to grow.  Food is transported in the form of dilute aqueous solution.  Transport of food from leaves to other parts of the plant is called translocation.

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APPENDIX:

Activity 6.7: Aim: To check the content of Haemoglobin. Steps


Visit a health centre in your locality and find out what is the normal range of haemoglobin content in human beings.

Normal range in male is 14–18 and in female is 13–16

Is it the same for children and adults?

In children it is more 15–20

Is there any difference in the haemoglobin levels for men and women?

Haemoglobin level in women is low

Visit a veterinary clinic in your locality. Find out what is the normal range of haemoglobin content in an animal like the buffalo or cow. Is this content different in calves, male and female animals? Compare the difference seen in male and female human beings and animals. How would explained?

the

difference,

if

any,

be

Activity 6.8: Aim: To check transpiration Steps Take two small pots of approximately the same size and having the same amount of soil. One should have a plant in it. Place a stick of the same height as the plant in the other pot. Cover the soil in both pots with a plastic sheet. Cover both sets, one with the plant and the other with the stick, with plastic sheets and place in bright sunlight for half an hour. Do you observe any difference in the two cases?

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So that moisture evaporation.

cannot

escape

by

Yes, there is a difference the plant has an adequate supply of water; the water which is lost through the stomata is replaced by water from the xylem vessels in the leaf. In fact, evaporation of water molecules from the cells of a leaf creates a suction which pulls water from the xylem cells of roots. The loss of water in the form of vapour from the aerial parts of the plant is known as transpiration.


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Excretion:  During the metabolic biochemical reactions, toxic wastes may be produced and water content of the body may increase or decrease.  Metabolic wastes include CO2, nitrogenous wastes like urea, uric acid, ammonia etc.  CO2 is thrown out of the body through the respiratory system.  Nitrogenous wastes along with excessive water are thrown out of body through excretory system.  Excretion is the biological process involved in removal of the excess or toxic wastes from the body.  Osmoregulation is the process of maintaining the right amount of water and proper ionic balance in the body.  The organs, which form, store and void the urine, constitute the urinary system or excretory system as seen in multicellular animals.  In unicellular organisms removal of wastes is done by simple diffusion from the body surface into the surrounding water. [This space is left intentional for student to draw diagram]

Human Excretory System

Excretion in Humans:  It is the system of organs and tissues that take part in the formation, storage, elimination of urine and excretion of nitrogenous waste products, water and some mineral salts.  It includes two kidneys, two ureters, a urinary bladder and a urethra.

Kidneys:     

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Kidneys are the urine-forming organs of vertebrates including mammals. The two flattened bean-shaped kidneys are located inside the abdomen. Each kidney is made up of excretory units called nephron. A nephron is essentially a long, coiled duct in which the coiling takes a definite course. A nephron along with the collecting tubule is also known as a uriniferous tubule. Each kidney possesses about 1 million nephrons in man.


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Efferent arteriole

PCT

DCT

Bowman’s capsule Glomerulus Renal artery

Collecting ducts

Afferent arteriole

Renal vein

Loop of Henle [This space is left intentional for student to draw diagram]

       

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A nephron has a cup shaped structure at the upper end called Bowman’s capsule. Glomerulus is a globular tuft of capillaries present in the cup shaped space of Bowman’s capsule. The afferent renal arteriole (arising from renal artery) enters the glomerulus and efferent renal arteriole leaves the glomerulus. Bowman’s capsule leads to tubular structures i.e. proximal convoluted tubule (PCT), Loop of Henle, distal convoluted tubule (DCT) and collecting ducts. The blood in the renal artery which contains nitrogenous waste products, enter the glomerulus. Blood is filtered from the blood capillaries into Bowman’s capsule. As the filterate passes through the tubular parts of nephrons, useful products such as glucose, amino acids are reabsorbed and are passed on to the blood capillaries. The nephrons ultimately drain the waste into a space inside kidney leading to ureter. Universal Tutorials – X CBSE (2012–13) – Biology

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This waste is called urine and contains water, nitrogenous waste products (mainly urea) and toxic substances.  Ureters drain the urine into urinary bladder where it is stored for some time.  Urine is thrown out of the body by a tube called urethra.

Excretion in Plants:  Plants use a variety of techniques to get rid of waste material.  Waste material may be stored in the cell-vacuoles or old xylem as gum and resin, removed in the falling leaves, or excreted into the surrounding soil.  Oxygen itself can be considered as a waste product generated during photosynthesis.  Excess of water is lost by transpiration. NCERT EXERCISE:

1) What criteria do we use to decide whether something is alive? 2) What are outside raw materials used for by an organism? 3) What processes would you consider essential for maintaining life? 4) What are the differences between Autotrophic and heterotrophic nutrition

5) Where do plants get each of the raw materials required for photosynthesis? 6) What is the role of the acid in our stomach? 7) What is the function of digestive enzymes? 8) How is the small intestine designed to absorb digested food? 9) How are fats digested in our bodies? Where does this process take place? 10) What is the role of saliva in the digestion of food? 11) What are the necessary conditions for autotrophic nutrition and what are its by–products? 12) What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration. [2005, 08]

13) How are the alveoli designed to maximise the exchange of gases? 14) Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans? 15) What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration? 16) What are the different ways in which glucose is oxidised to provide energy in various organisms? [2008] 17) How is oxygen and carbon dioxide transported in human beings? [2008] 18) How are the lungs designed in human beings to maximise the area for exchange of gases? [2008]

19) What are the components of the transport system in human beings? What are the functions of these components? 20) Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

21) What are the components of the transport system in highly organized plants? 22) How are water and mineral transported in plants?

23) How is food transported in plants? 24) What would be the consequences of a deficiency of haemoglobin in our bodies? 25) Describe double circulation in human beings. Why is it necessary? Volume


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26) 27) 28) 29)

What are the differences between the transport of materials in xylem and phloem? Describe the structure and functioning of nephrons. What are the methods used by plants to get rid of excretory products? How is the amount of urine produced regulated.

30) Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning. 31) Multiple Choice Questions: i) The kidneys in human beings are a part of the system for a) nutrition b) respiration c) excretion d) transportation ii) The xylem in plants is responsible for a) Transport of water b) Transport of food c) Transport of amino acids d) Transport of O2 iii) The autotrophic mode of nutrition requires a) carbon dioxide and water b) chlorophyll. c) sunlight d) all of the above. iv) The breakdown of pyruvate to give carbon dioxide, water and energy takes place in a) cytoplasm b) mitochondria c) chloroplast d) nucleus PREVIOUS BOARD QUESTIONS: Very Short Answer type Questions: [1 Mark] Nutrition: 1) Where does digestion of fat takes place in our body? [2009] 2) What process in plants is known as transpiration? [2008] 3) Write the mode of nutrition in fungi. [2005] 4) Give an example of a vestigial organ present in human body. [2004] 5) Name the site of photosynthesis. [2004] Respiration: 6) What is breathing? [2006] Transportation: 7) What will happen to a plant if its xylem is removed? [2009] 8) Name the tissue which transports soluble products of photosynthesis in a plant. [2008] 9) Name the term for transport of food from leaves to other parts of the plant. [2007] 10) Name the type of blood vessels which carry blood from organs heart. [2006] 11) Name the largest artery in the human body. [2005] Excretion: 12) Name the excretory unit of a kidney [2007] Short Answer type Questions: [2 Marks] Nutrition: 13) Draw the diagram of cross–section of a leaf and label the following in it: i) Chloroplast ii) Guard cell iii) Lower epidermis iv) Upper epidermis [2006] 14) How does absorption take place in the small intestine of the human beings? [2005] 15) Leaves of a healthy potted plant were coated with Vaseline to block the stomata. Will this plant remain healthy for long? State three reasons for your answer [2004] Transportation: 16) Point out two differences between an artery and a vein. [2007] 102


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17) What do you mean by double circulation of blood? [2007] Excretion: 18) State the two vital functions of the human kidney. Name the procedure used in the working of artificial kidney. [2007] Short Answer type Questions: [3 Marks] Nutrition: 19) Write the functions of the following in the digestive process i) Bile ii) Pancreatic amylase. [2006] 20) How do each of the following factors affect the productivity in the process of photosynthesis? i) Temperature ii) Water iii) Carbon dioxide [2005] Respiration: 21) Give reasons for the following: i) The lung alveoli are covered with blood capillaries. ii) The wall of trachea is supported by cartilage rings. [2006] 22) Label parts 1 to 5 in the given diagram of the Human Respiratory System. [2006]

2

23) State the role of the following in the human respiratory system: i) Nasal cavity ii) Diaphragm iii) Alveoli [2006] Transportation: 24) Name the constituents of blood. Why white blood corpuscles are called ‘soldiers of the body’? [2005] 25) Name three kinds of blood vessels of human circulatory system. Write the function of each. [2005] 26) Write important functions of the blood. [2004] Excretion: 27) Label parts 1 to 6 in the given figure of the Excretory System in human beings. [2005]

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28) What happens to glucose, which enters the nephron along with filtrate during excretion in human beings? State two vital functions of kidney. [2005] 29) With the help of a diagram describe the process of urine formation in nephron of human kidney. [2004] Long Answer type Questions: [5 Mark] Nutrition: 30) a) Draw a diagram of human alimentary canal and label on it: Oesophagus, Gall Bladder, Liver and Pancreas. [2009] b) Explain the statement “Bile does not contain any enzyme but it is essential for digestions. 31) a) Draw a diagram of Excretory system in human being and label on it: Aorta, Vena Cava, urinary bladder, urethra. b) List two vital system of Kidney. [2009] 32) a) Draw a diagram depicting Human Alimentary Canal and label on it: Gall Bladder, Liver and Pancreas. b) State the roles of Liver and Pancreas. c) Name the organ which performs the following functions in humans: i) Absorption of digested food ii) Absorption of water [2008] 33) a) Draw a diagram of human ‘alimentary canal’. Label the following on the diagram drawn: Oesophagus, Liver, Gall bladder, Large intestine b) What is the function of liver in the human body? [2007] 34) Take 1 mL starch solution in two test tubes A and B. add 1 mL saliva to test tube A and leave both test tubes undisturbed for half an hour. Now add a few drops of dilute iodine solution to the test tubes. On the basis of your observations, answer the following questions i) In which test tube do you observe a colour change? ii) What does this indicate about the presence or absence of starch in the action of saliva on starch? [2007] 35) Define the terms ‘nutrition’ and ‘nutrients’. List two differences between ‘Holozoic nutrition’ and ‘Saprophytic nutrition’. Give two examples each of these two types of nutrition. [2005] 36) Explain the process of digestion of food in the alimentary canal. [2005] 37) Explain the process of ‘photosynthesis’ in plants. List four factors which influence this process and describe how each of them affects the rate of photosynthesis process. [2005] 38) Name the main organs of human digestive system in the order in which they are involved in digesting food. In what steps and how does digestion of carbohydrates and proteins take place in our bodies? [2004] Respiration: 39) A student takes some fruit juice or sugar solution and adds some yeast to it. He takes this mixture in a test tube fitted with a one-hold cork. He then fits the cork with a bent glass tube and dips the free end of the glass tube into a test tube containing freshly prepared lime water. Now answer the following questions i) What change is observed in the lime water? ii) Name and explain the process taking place. iii) Write the chemical formula for the products so formed. [2004] Transportation: 40) a) Draw a sectional view of the human heart and label on it Aorta, Pulmonary arteries, Vena cava, Left ventricle. [2009] b) Why is double circulation of blood necessary in human beings? [2009

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41) a) Draw a sectional view of the human heart and label on it: Aorta, Right Ventricle and Pulmonary Veins. b) State the functions of the following components of transport system: i) Blood ii) Lymph [2008] 42) How does blood circulate between lungs and heart in human beings? Give two functions of lymph in the human body. [2006] 43) Draw a diagram of human heart and label the following on it: i) Aorta ii) Pulmonary artery and vein iii) Septum iv) Vena cava [2005] 44) i) Name the blood vessel that brings oxygenated blood to the human heart. ii) Which chamber of the human heart receives oxygenated blood? iii) Explain how oxygenated blood from this chamber is sent to all parts of the body. [2004] Excretion: 45) a) Draw the structure of a nephron and label the following on it. Glomerulus, Bowman’s Capsule, Renal artery, collecting duct. b) What happens to glucose that enters the nephron along the filtrate? [2009] 46) a) Draw a diagram of the human urinary system and label in it i) Kidney ii) Ureter iii) Urinary bladder iv) Urethra b) Name the two major components of normal human urine. [2006] MISCELLANEOUS EXERCISES: Very Short Answer type Question: [1 Mark] Nutrition: 1) Define life processes. 2) Name the secretion of liver. 3) Define nutrition. What are the different modes of nutrition? 4) What are nutrients? 5) Define heterotrophs. 6) What is primary source of energy of living organisms? 7) Where does mastication of food occur? 8) Which carbohydrate is not digested by man? 9) How the food is made alkaline in small intestine? 10) How is the unused energy stored in plants and animals? 11) What is diffusion? 12) What is chlorophyll? 13) What are the essential requirements for photosynthesis? 14) What is the source of oxygen liberated in photosynthesis? 15) What would happen if all the green plants disappear from earth? 16) Give the overall equation of photosynthesis. 17) Define digestion. 18) Name an organ of alimentary canal where fat is digested. 19) Where does complete digestion of fats, carbohydrates and proteins takes place? 20) Why simple diffusion is not possible in multicellular organisms? 21) Name one gland of the human body which secretes digestive enzymes as well as hormones. 22) What is heterotrophic nutrition? 23) What is the mode of nutrition found in Amoeba? 24) Mention two structural features of the small intestine, which adds to its absorptive capacity? Volume


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25) Mention the role of bile salts in the digestion of fats. 26) Define phagocytosis. 27) Why can’t insects carry out gaseous exchange through their body surface? 28) Give two examples of plant organisms which carry out heterotrophic nutrition 29) What is holozoic nutrition? 30) Is food vacuole of Amoeba, temporary structure or a permanent one? 31) What are the complete photosynthetic units of plants? 32) What are the end products of photosynthesis? Respiration: 33) Define respiration. 34) What is the other term given for anaerobic respiration? Which human tissue respires anerobically during running? 35) Which products of respiration would be seeing in mitochondrial cells? 36) What is the main outcome of respiration? 37) What is fermentation? 38) Which part of roots is involved in exchange of respiratory gases? 39) Name two organisms which respire anaerobically. 40) What happens to the carbondioxide which collects in human tissue? 41) Why do the land plants die if their roots are submerged in water? Transportation: 42) Define transportation. 43) What is transpiration? 44) Which cells control the opening and closing of stomata? 45) Define Blood. 46) What is lymph? 47) Give example of single circulation. 48) Name two fluids present in our body. 49) Why is blood red in colour? 50) What is the function of lymphatic system? 51) Where does the cardiac impulse originate? 52) Why the walls of arteries are thick and walls of veins are thin? 53) Why do veins have valves? 54) What is transpirational pull? 55) Name the part of plant through which water is lost in the form of water vapours. 56) Name the tissue through which translocation of food takes place. 57) Name the following: i) The membrane that encloses heart. ii) The valve present between right atrium and right ventricle. iii) The valve present between left atrium and left ventricle. iv) The blood vessel that takes away oxygenated blood from heart. v) An artery which carries impure (deoxygenated) blood. vi) A vein in the human body which carries oxygenated blood. vii) The respiratory pigment contained in human blood. viii) Minute blood vessels which join arteries and veins. ix) The fluid part of the blood. x) A liquid tissue found in the human body. 106


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58) Name the system responsible for transportation of materials in human beings. 59) What do you mean by ‘translocation’ with respect to transport in plants? Excretion: 60) Define excretion. 61) What is urethra? 62) Name the following: i) A process by which the unwanted nitrogenous wastes are eliminated from the body. ii) Major excretory organs of man. iii) The structural and functional units of kidney. iv) The structure that brings urine from the kidney to the urinary bladder. v) Thin membranous sac serving as the reservoir of urine. vi) Any two organic constituents of normal human urine. vii) The chief nitrogenous waste product in the human urine and the organ which produces it. 63) Where is urine carried through the ureters? Short Answers type of Questions: (2–3 Marks) Nutrition: 64) Trypsin acts at an alkaline pH. What provides this alkalinity? Give the action of trypsin. 65) How would it affect the digestion of proteins and carbohydrates in the duodenum of a man if there were a blockage in the pancreatic duct? Explain. 66) How would non-secretion of saliva affect digestion of food in our mouth? 67) How would the digestion of food be affected if the bile duct is completely blocked? Explain. 68) What are the events occurring during photosynthesis? 69) Describe the large intestine 70) Discuss the fate of food in the oral cavity of man. 71) Why does a piece of bread start tasting sweet after chewing for some time? 72) What are the various structures seen in buccal cavity of man? 73) What are the functions of tongue? 74) What do you understand by parasitic nutrition? 75) Differentiate between respiration and photosynthesis. 76) Describe the role of intestinal juice. Respiration: 77) How do the leaves, roots and stems respire? 78) How does the exchange of gases take place in plants? 79) How are inspiration and expiration brought about in humans? 80) What are the characteristics of a respiratory organ? 81) How is carbon dioxide transported from various cells to the lungs in our body? 82) Give scientific reasons for the following: i) Respiration is called an energy releasing process. ii) The actively growing parts of the plants show maximum rate of respiration iii) Glucose is incompletely oxidized during anaerobic respiration. iv) Amount of energy released during anaerobic respiration is less as compared to that released during aerobic respiration v) When you do vigorous exercise at the gym you may experience cramps in your leg muscles. Why does this happen? 83) What are the requirements of a surface to be highly efficient for gaseous exchange? 84) Why is it harmful to respire through mouth than through nasal openings? 85) Give two points of difference between respiration in plants and respiration in animals. Volume


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Transportation: 86) State the functions of stomata. 87) Explain the major features of human lymphatic system. 88) Why is transportation of materials necessary? 89) What are the important functions of circulatory system? 90) Name the vascular tissue of plants with function. 91) How transpiration is useful to plants? Excretion: 92) How do kidneys conserve water when the water content of the body is low? 93) Which is the major nitrogenous waste product in a human being? How is it removed from the body? Long Answers type Questions: (5 Marks) Nutrition: 94) Write a note on various modes of nutrition in animals. 95) Explain Nutrition in Amoeba. 96) Describe the digestion of proteins step by step as they pass through the food canal in humans. Respiration: 97) Explain how CO2 is carried in the blood and released in the lungs? 98) How is oxygen transported in the blood and released in the tissues? 99) Describe the process of absorption of water into the roots. 100) Describe how the respiratory gases are exchanged between blood and alveolar? Transportation: 101) Explain working of Heart. 102) Explain blood vessels. 103) Explain absorption of water by plants. 104) i) Draw the diagram of heart and label its four chambers. ii) Construct a table to show the functions of these four chambers. Excretion: 105) i) Draw the diagram of excretory system of human being and label four major parts. ii) Construct a table to show the functions of these four parts. 106) How is the structure of kidney related to the function of excretion? Describe the process of urine formation in humans. MULTIPLE CHOICE QUESTIONS: PRACTICAL THEORY

Preparation of Temporary Mount: 1) Stomata help in exchange of ______ with air a) oxygen b) carbon dioxide c) water vapour d) all of them 2) In cereals stomata are present a) on upper surface of leaves b) on lower surface of leaves c) on both the surface of leaves d) on margin of the leaves 3) Woody plants carry gaseous exchange through a) root hair b) stem hair c) lenticels d) epidermal cells 4) Epidermis consists of a single layer of cells which are irregular in outline and ___. a) with intercellular spaces b) without intercellular spaces c) with intracellular spaces d) without intracellular spaces

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5) What would be the precaution to be taken while preparing a temporary mount? a) Avoid curling of peel b) Peel should not be dry c) Avoid the entry of air bubbles d) all of them 6) What is the aim of this experiment “preparation of temporary mount”? a) To show respiration takes place b) To show Photosynthesis is carried out c) To show the presence of stomata d) None of the above 7) A plant whose stomata open during night and close by day a) tradescantia b) mango c) bryophyllum d) hydrilla 8) Which surface of dicot leaf has stomata? a) on upper surface b) on lower surface c) on both the surfaces d) on the margin 9) On which factor opening of stomata depends? a) Turgor pressure b) Root pressure c) Osmotic pressure d) None of them 10) Why should the peel be taken from the lower surface of the leaf. a) Because lower surface is loosely attached b) there is spongy parenchyma present c) More stomata are present on lower epidermis d) all the above 11) Why should we use thin leaf to study the structure of a leaf? a) Thin leaf is much easier than thick leaf b) More stomata are found in thin leaf c) Thin leaf will provide clear view of its surface d) None of the above 12) Presence of sunken stomata is the characteristic feature of a) hydrophytes b) mesophytes c) halophytes d) xerophytes 13) If you stain the leaf Peel with iodine solution, the part which turn blue black is a) cytoplasm b) guard cells c) cell wall d) vacuole 14) Colour of guard cells is: a) Yellow b) Brown c) Green d) White 15) The inner wall of guard cells facing stomata is: a) thin b) elastic c) thick d) of normal size 16) The correct labeling of the diagram given below: a) (i) stomatal pore (ii) guard cells i b) (i) subsidiary cells (ii) stomata c) (i) epidermal cells (ii) stomata ii d) None of these 17) Guard cells differ from epidermal cells in: a) dense protoplasm b) shape c) differential thickenings of cell wall d) all of these 18) Stomata are either absent or functionless in a) Apple b) potato c) water lily d) hydrilla 19) The stomatal apparatus are made up of a) Guard cell and subsidiary cell b) Guard cell; subsidiary cell and stomatal aperture c) Stomatal Aperture and Guard cell d) Guard cell and subsidiary cell; Stomatal aperture and Epidermis 20) The peel of leaf is kept in water before staining: a) to increase the quantity of water b) to prevent it from drying c) to keep chemical reactions alive in cell d) none of these Volume


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21) Which part of cell is coloured by safranin: a) nucleus b) cytoplasm c) cell wall d) all of these 22) The part of leaf having stomata distributed is: a) epidermis b) cuticle c) parenchyma tissues d) conducting tissues 23) Stomata are open: a) during daytime b) at night c) all the time d) none of these 24) Glycerine is used in experiment to keep the peel of leaves a) clear b) moist c) dry d) none of these 25) A student draws the following sketch of stomatal apparatus and numbers the parts to label them. The chloroplast is denoted by a) 1 b) 2 c) 3 d) 4 26) When students observed a stained epidermal peel of a leaf under the microscope, it appeared pinkish red. The stain used was, a) iodine b) acetocarmine c) safranin d) Colchicin 27) The inorganic substance helping in opening and closing of stomata are: a) sodium ion b) magnesium ion c) potassium ion d) sulphur ion 28) Which is the most common chlorophyll found in plants? a) chlorophyll d b) chlorophyll e c) chlorophyll a d) chlorophyll c 29) Given below are the steps in the preparation of a temporary mount of a stained leaf peel. i) Cover the material with the cover slip. ii) Transfer the stained peel to the clean glass slide and add a drop of glycerine. iii) Remove the peel from the ventral surface of the leaf. iv) Drop it in the water in a petri dish and add a drop of safranin stain. The correct sequence of steps is a) iii, iv, ii, i b) i, ii, iii, iv c) ii, iii, iv, i d) iii, iv, i, ii 30) Exchange of gases through stomata for the purpose of photosynthesis occurs across the surface of a) stems b) roots c) leaves d) all of them 31) The correct procedure to prepare a temporary mount of a stained leaf epidermis is A B C D Take the peel of a leaf Take a peel of a leaf; Stain the leaf; Take a peel; Stain it with safranin; Wash it in water; Take a peel; Stain it with iodine; Transfer the peel to the Place it on the slide; Wash the peel in Transfer the peel to slide; Add a drop of water; the slide; glycerin on it; Remove the excess Place it on a slide; Remove excess stain Put a cover slip stain; with blotting paper; Put a cover slip on gently; Put a cover slip on it it Put a cover slip on it; a) A b) B c) C d) D

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2) Leaf is boiled in which of the following solvent to remove chlorophyll? a) water b) iodine solution c) alcohol d) none of these 3) Photosynthesis occurs in: a) chloroplast b) mitochondria c) cytoplasm d) cell wall 4) A part of de–starched leaf of a potted plant was covered with black paper strips on both sides and the plant was kept in sunlight for 8 hours. The leaf was then tested with iodine after boiling it in alcohol. Only the uncovered part of the leaf turned blue black. The inference is that: a) CO2 is necessary for photosynthesis b) light is necessary for photosynthesis c) chlorophyll is necessary for photosynthesis d) water is necessary for photosynthesis 5) Iodine gives blue black colour with leaf due to: a) chloroplast b) chlorophyll c) starch d) fats 6) The end products of Photosynthesis are: a) glucose b) oxygen c) starch d) glucose and oxygen 7) A destarched potted plant was kept in sunlight for a few hours after applying a coat of vaseline on both the surface of leaf. The leaf was then decolourised and tested for starch. Which of the following statements will be true in this case a) leaf turned blue black on upper side b) leaf turned blue black on lower side c) leaf did not turn blue black d) leaf turned blue black 8) Why the covered region does not show the presence of starch? a) It does not receive light b) Photosynthesis does not occur c) both ‘a’ and ‘b’ d) None 9) It is essential to decolourise the leaf before testing for starch because a) test for glucose can be easily performed b) starch reacts with chlorophyll c) presence of blue black colour cannot be detected without decolouring the leaf d) presence of blue black colour can be detected without decolouring the leaf 10) I2 solution turns the following blue black a) sugar b) starch c) both a and b d) oil 11) Which is the correct equation of photosynthesis? Sunlight a) 6CO2 + 6H2O  → C6H12O6 + 6O2

Mitochordria b) 6CO2 + 6H2O    → C6H12O6 + 6O2

c) 4CO2 + 6H2O  → C6H12O6 + 4O2

d) 6CO2 + 6O2  → C6H12O6 + 6CO2

Chlorophyll

Sunlight

Chlorophyll

Sunlight

Chlorophyll

12) In which one the following cases will the leaf show a positive starch test a) leaf kept in dark for 24 hours and then discoloured b) leaf kept in sunlight but not discoloured c) leaf kept in sunlight and then discoloured d) leaf discoloured and then kept in sunlight 13) In an experiment on photosynthesis, a student fixed a strip of black paper on the dorsal surface of a Bougainvillea leaf in the morning. In the evening she tested the leaf for starch. The result was a) the dorsal surface of the leaf was white but the ventral surface turned blue. b) both the surfaces of the covered portion remained white. c) the entire leaf turned blue black. d) the entire leaf remained white.

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14) Which is the internal factor affecting photosynthesis? a) Light b) Temperature c) Chlorophyll d) Carbon Dioxide 15) Why leaf is boiled in alcohol? a) To remove the chlorophyll b) To decolourize the leaf c) To remove starch d) both ‘a’ and ‘b’ 16) What are the various pigments found in plants? a) chlorophyll b) carotenoids c) both ‘a’ and ‘b’ d) None 17) Which is the most common chlorophyll found in plants? a) chlorophyll ‘a’ and ‘b’ b) chlorophyll ‘a’ and ‘c’ c) chlorophyll ‘d’ and ‘e’ d) chlorophyll ‘b’ and ‘d’ 18) What is the function of light reaction? a) Trapping of energy by chlorophyll b) splitting H2O molecules into hydrogen and oxygen c) To produce ATP d) all of the above 19) How is energy stored in leaves? a) ADP b) NADP c) ATP d) NADPH 20) What is the optimum temperature for maximum photosynthesis? a) 30° C b) 35° C c) 40° C d) 45° C 21) Photosynthesis is seen in a) Euglena b) Cyanobacteria c) Plants d) All of the above 22) A student performed the starch test on a leaf. Some steps involved are shown below.

The correct sequence of steps should be a) iv; iii; ii; i b) i; ii; iii; iv c) ii; iii; iv; i d) i; iii; iv; ii 23) Rate of photosynthesis is independent of a) Intensity of Light b) CO2 c) Photoperiod d) O2 24) In an experiment to show that sunlight is necessary for photosynthesis, the leaf is boiled in alcohol for a few minutes using a water bath. It is essential because a) alcohol does not vapourize quickly b) steam from the water bath heats the leaf rapidly c) steam from the water bath dissolves the chlorophyll d) alcohol is flammable 25) Dark reaction of photosynthesis occurs in: a) stroma b) nucleus c) cytoplasm d) grana

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26) A healthy potted plant was kept in dark for 48 hours. One of its leaf was totally covered by a black paper except three regions as shown in figure and the plant was kept in light for 10 hours. After wards this leaf was tested for the presence of starch using alcohol, water and iodine solution. What colour will be observed in the leaf at various regions–triangle / circle / star / rest of leaf? a) triangle, circle and star white / rest of the leaf blue b) triangle, circle and star blue / rest of the leaf white c) triangle and circle white / star blue / rest of the leaf green d) triangle and circle blue / star white / rest of the leaf green. 27) Evolution of O2 from water (H2O) in photosynthesis is a: a) light reaction b) dark reaction c) both dark and light reaction d) none of these 28) Light reaction of photosynthesis occurs in: a) cytoplasm b) nucleus c) grana d) stoma 29) Products of Photosynthesis are a) ATP and NADP b) ADP and NADP c) ATP and NADPH d) ADP and NADPH 30) Fixation of CO2 to form glucose in photosynthesis is a: a) dark reaction b) light reaction c) both dark and light reaction d) none of these 31) After boiling the leaves in alcohol and washing with water, which of the following solution is added on them? a) iodine solution b) saline solution c) sugar solution d) starch solution

Respiration: 1) The products of anaerobic respiration is: a) CO2 and glucose b) O2 and alcohol c) CO2 and water d) CO2 and alcohol 2) The apparatus set up in the above experiment is airtight to keep: a) fixed amount of O2 b) fixed amount of CO2 c) partial vacuum d) none of these 3) Anaerobic respiration occurs in: a) mitochondria b) cytoplasm c) both mitochondria and cytoplasm d) none of these 4) Seeds taken in the flask during respiration experiment are: a) germinating b) dry c) just wet d) none of these 5) In the experiment the function of KOH is to absorb: a) water vapour b) oxygen c) CO2 d) air 6) Which of the following statement is incorrect in case of Aerobic respiration? a) It is incomplete oxidation of food b) It takes place in presence of oxygen c) It occurs in mitochondria d) It releases energy 7) The rising of H2O level in the experiment of respiration shows that a) CO2 is produced by germinating seeds b) CO2 produced is absorbed by potassium hydroxide of the specimen tube c) O2 is released by germinating seeds d) both ‘a’ and ‘b’ 8) What precautions to be kept in mind while performing the experiment for respiration? a) Apparatus should be air tight b) Germinating seeds should not have any green part c) Germinating seeds should be water soaked d) all the above Volume


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9) Correct chemical equation to represent respiration is a) 6CO2 + 6H2O  → C6H12O6 + 6O2 Sunlight

b) C6H12O6 + 6O2 → 6H2O + CO2 + energy

c) C6H12O6 → 6CO2 + 6H2O + 38ATP d) C6H12O6 + 6O2 → C2H5OH + 2CO2 + energy 10) What precaution to be taken, if the germinating seeds are replaced by buds? a) Conical flask must be covered by black paper b) Apparatus should be air tight c) Buds should not have any green part d) All of the above 11) How much energy is released by oxidation of one glucose molecule? a) 35 ATP b) 36 ATP c) 37 ATP d) 38 ATP 12) Identify the organism which respire anaerobically. a) Bacteria b) Fungi c) Yeast d) All the above 13) Aerobic respiration occurs in: a) mitochondria b) chloroplast c) golgi body d) none of these 14) The substance used to make all connections air–tight in the experiment to show that CO2 is produced during respiration is: a) Vaseline b) wax c) butter d) none of these 15) The source of energy in respiration is a) Starch b) Alcohol c) Sunlight d) Glucose 16) The energy produced during respiration is stored in the form of a) ADP b) NADP c) ATP d) HTP 17) Respiration is: a) oxidation process b) reduction process c) endothermic process d) None of these 18) After performing the experiment to show that germinating seeds give out carbon dioxide during respiration, students drew the following diagrams. The correct labelled diagram is

A)

B)

C)

D)

a) A b) B c) C d) D 19) Take some freshly prepared lime water in a test tube. Blow air through this lime water. What would be the observation? a) Lime water remains same b) Lime water turns milky c) Lime water turns yellow d) Lime water will start smelling. 20) A student sets up the apparatus for the experiment to show that CO2 is released during respiration. After 2 hours, he would observe a) KOH turning milky b) water level rising in the bent tube in the beaker c) water level decreasing in the bent tube in the beaker d) water turning turbid in the beaker. 21) When does lime water turn milky? b) when lime water comes in contact with CO2 a) when O2 is absorbed c) when it comes in contact with atmosphere d) both ‘b’ and ‘c’ 114


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22) In an experiment shown in the figure, water is found to rise in the bent tube. The reason is that a) seeds use up oxygen in the flask b) carbon dioxide is given out by the germinating seeds. c) germinating seeds attract water from the beaker d) seeds use oxygen and release carbon dioxide which is absorbed by potassium hydroxide. 23) Respiration did not occur in the set up given below a) roasted peanuts are not present in adequate amount b) roasted peanuts do not contain respiring living cells c) roasted peanuts produce negligible quantity of CO2 d) none of the above 24) Identify the fault in the setup for proving that CO2 is produced during respiration a) ethyl alcohol should be taken instead of KOH b) test tube containing KOH is not fully filled c) end of the delivers’ tube inside the flask is not touching the germinating seeds d) other end of the delivery tube is not completely dipped in water 25) Lime water in an indicator of CO2. Why is then lime water not taken in the set up for respiration? a) Lime water is a harmful chemical. It releases toxic gases which harm the seeds. b) Lime water may turn milky due to the CO2 already present in the flask before the respiration of seeds c) Lime water turns milky very slowly and hence cannot be used to indicate the process of respiration d) None of the above 26) Kreb cycle takes place in a) cytoplasm (b) mitochondria c) ribosomes (d) Nucleus 27) Site of glycolysis in cell a) cytoplasm b) mitochondria c) nucleus d) ribosomes 28) The water level did not change when germinating seeds with green portions were taken in the set up for respiration. This was because a) green portion inhibit the process of respiration b) green portion respire anaerobically c) the CO2 produced during respiration by seed was used up in photosynthesis by green portion d) none of the above

Endosmosis in Raisins: 1) Which of the following is not correct regarding the absorption of water by raisins? a) petridish must have sufficient water b) weighing must be accurate c) raisins must be wiped off gently before taking final weight d) raisins must not have stalks

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2) The cell organelle acting as semi–permeable membrane: a) cell wall b) cell membrane c) cytoplasm d) nucleus 3) Water moves from higher concentration to lower concentration through semi–permeable membrane in: a) osmosis b) diffusion c) circulation d) plasmolysis 4) In the above experiment 10 dry raisins were weighed and then soaked in water and weighed again after 4 hours. The formula for calculating % of water absorbed by raisins is W2 − W1 × 100. Following observations are noted: W1

5)

6)

7)

8)

9)

10)

Weight of 10 dry raisins = 7.8 g; Weight of 10 raisins after 4 hours = 14.2 g. Calculate % of water absorbed by raisins and select the correct answer out of the following which matches with your answer: a) 55% b) 82% c) 18% d) 100% What would be the definition of endosmosis. a) When water moves from higher concentration to lower concentration through semipermeable membrane b) When water from inside the cell moves outside through semipermeable membrane c) When water from outside the cell moves inside through semipermeable membrane d) Movement of water from higher concentration to lower concentration What are the precautions to be taken to perform endosmosis experiment? a) Raisins should be completely immersed in water for sufficient time b) Before soaking in water raisins should be weighed properly c) Before weighing remove extra water from raisins with the help of filter paper. d) all the above What will happen if raisins are kept in isotonic solution? a) Movement of water will not occur b) the raisins will not gain water c) the raisins will not lose water d) all the above Factors that affect rate of osmosis are a) Concentration of solution b) temperature c) Wind d) a and b Which statement is correct in case of diffusion? a) solvent particles move b) semi permeable membrane is present c) solute particles move d) None of them The formula for calculating % of water absorbed by raisins is W − W2 W2 − W1 W2 − W1 W − W2 a) × 100 b) 1 × 100 c) 1 × 100 d) × 100 W1 W1 W2 W2

11) Students A, B and C were given five raisins each of equal weight. The raisins were soaked in distilled water at room temperature. A removed the raisins after 20 minutes, B after two hours and C after 40 minutes. If PA, PB and PC denote percentage absorption of water obtained by students A, B and C respectively, then a) PA > PB > PC b) PA < PB < PC c) PA < PB > PC d) PA = PB = PC 12) A student dissolved 5 g of sugar in 100 mL of distilled water in beaker A. She dissolved 100 g of sugar in100 mL of distilled water in beaker B. Then she dropped a few raisins of equal weight in each beaker. After two hours she found the raisins in A swollen and those in B shrunken. The inference drawn is that a) sugar concentration of raisins is lower than that of solution A and higher than that of solution B b) sugar concentration of raisins is higher than that of solution A and lower than that of solution B c) in B the cell membrane of raisins was damaged resulting in leaching d) in A the permeability to water of the cell membrane of raisins was enhanced 116


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13) A student dissolved 1 g of sugar in 10 ml of distilled water in a beaker A. He dissolved 10 g of sugar in 100 ml of distilled water in beaker B. Then he dropped a few raisins, in each. After two hours he found the raisins a) swollen in A and shrunken in B b) shrunken in A and swollen in B c) swollen in both d) shrunken in both 14) What precaution should be taken to perform the experiment of raisins? a) Raisins should be clean b) Raisins should be fresh c) Raisins must be with intact stalks d) All of (a, b, c) 15) The significance of osmosis in plants is a) It helps in absorption of water by the root hair b) It controls the opening and closing of stomata c) Cell to cell movement of water throughout the plant body occurs through osmosis d) all of these 16) Process of osmosis occurs in which of the following: a) swelling of raisins in water b) excretion in amoeba c) adding salt to pickle d) All of these 17) A student soaked 10 g of raisins in 50 ml of distilled water in two beakers A and B each. She maintained beaker A at 25°C and beaker B at 50°C. After an hour, the percentage of water absorbed will be a) the same in both A and B b) more in A than in B c) more in B than in A d) Exactly twice as much in B as in A 18) In a solution A, 50g of sugar is mixed in 100 ml of water and in solution B, 25g of sugar is mixed in 50 ml of water. If both the solutions are separated by a semipermeable membrane the net movement of water will be from a) A to B b) B to A c) no movement d) none of the above 19) What is the nature of raisins seen in this diagram? a) shrunken b) swollen c) dried d) flaccid 20) Which of the following process occurs when the grapes are kept in hypertonic solution? a) exosmosis b) endosmosis c) both exosmosis and endosmosis d) none of these 21) Which of the following figures best describes the condition of raisins when dipped in solution A containing 2.5 g of sugar in 25 ml of water and solution B containing 2.5 g of sugar in 250 ml of water.

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22) Shrinking of cytoplasm and vacuole of a plant cell when placed in a hypertonic solution is called a) plasmolysis b) deplasmolysis c) Activation d) none of the above 23) A plant cell is placed in a hypertonic solution. Which of the following diagrams best represent the change in the plant cell due to hypertonic solution?

(I)

(II)

a) I b) II c) I and II d) none of these 24) 5 raisins each were put in 3 solutions A, B and C. After 2 hours it was seen that

B

i) Size of raisins did not change in ‘A’ ii) Raisins became swollen in ‘B’ iii) Raisins shrunk in ‘C’ Which of the following statements is true about the 3 solutions with respect to the cell sap of raisin a) A is isotonic, B is hypotonic, C is hypertonic b) A is isotonic, B is hypertonic, C is hypotonic c) A is hypotonic, B is hypertonic, C is isotonic d) A is hypertonic, B is isotonic, C is hypotonic 25) A solution having such a solute concentration that it gains water by osmosis across a semipermeable membrane from some specified solution a) Hypertonic solution b) Hypotonic solution c) Isotonic solution d) none of the above 26) A student dissolved 100 g of sugar in 100 ml of water in a beaker and then dropped a few raisins in it. After 2 hours raisins were found to have shrunken, this happened because a) B is hypotonic to sap in raisins b) B is hypertonic to sap in raisins c) B is isotonic to sap in raisins d) none of the above 27) Raisins each were put in 3 solutions X Y and Z solution X was hypotonic to cell sap of raisins solution Y was hypertonic to cell sap of raisins solutions Z was isotonic to cell sap of raisins. The condition of raisins in 3 solutions is best represented as a) Raisins swell up in X, raisins shrink in Y and raisins remain unchanged in Z. b) Raisins shrink in X, raisins swell in Y and raisins remain unchanged in Z c) Raisins remain unchanged in X, raisins swell in Y and raisins shrink in Z d) Raisins remain unchanged in X, raisins shrink in Y and raisins swell in Z

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Chapter 07: Control and Co-ordination Chapter Map: Coordination in Plants and Animals Coordination in Animals Human Nervous System Neurons Components of Nervous System Central Nervous System Peripheral Nervous System

Reflex Action Hormones Coordination in Plants

Co–ordination in Plants and Animals:  Every organism has a property called irritability to show a response to its environmental changes.  An environmental change is known as stimulus.  Organisms respond in various ways to these stimuli due to the fundamental property of their protoplasm to get excited or irritated.  Plants lack specialized structures for perception of external stimuli.  Animals have specialized cells called neurons.  Neurons are the structural and functional unit of the nervous system.  The system that receives stimulus transmits it to other parts of the body, and the correspondingly produce effects are known as nervous system.  Nervous system (includes the brain, spinal cord and nerves) receives information from the surroundings, processes and interprets it and responds accordingly and passes information from one internal system to another.  Nervous system and endocrine system (related to hormones) together control and coordinate various functions of the body.

Coordination in Animals:  Multicellular animals have specialized cells or structures to respond to stimuli.  These specialized cells are called receptors. These are Volume


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

   

 photoreceptors (for light) e.g. eye  phonoreceptors (for sound) e.g., ear  olfactoreceptors (for smell) e.g. nose and  gustatory receptors (taste) e.g. tongue. It is a system of neurons, nerves and nerve organs which controls, links and co-ordinates the activities of different organs of the body of an animal to make it an integrated whole which can also show adjustments according to its environment. Brain is a centre for the analysis of information such as those related to hearing, vision, smell, taste, movement, flight and other muscular actions Nervous system of vertebrates consists of central nervous system and peripheral nervous system. Higher vertebrates like birds and mammals have specific specialized areas of brain, which provide the ability for learning and memory. Besides nervous system, hormones secreted by endocrine glands, help in control and coordination of various functions in animals.

Human Nervous System:  In the human beings two types of system are present to perform the function of control and coordination. These are:  Nervous System  Endocrine system  Nervous system and endocrine system works together to control and coordinate all the human activities.

Function of Human Nervous System:  The functions of the nervous system are listed below:  Nervous system:  Receives message from the sense organ [like eyes, ears, nose, skin, tongue].  Analyses the message and decides the action to be taken  Sends instructions to the muscles of the concerned body parts for necessary action  Nervous system controls and coordinates the activities:  Which we think such as: reading, writing, dancing etc.  Which we do not think such as: breathing, heart beat etc.  Nervous system passes information from one internal system to another. For example: as soon as we put food in our mouth, nervous system sends a signal to the salivary gland to release saliva in the mouth cavity [buccal cavity].  Nervous system controls our memory and thinking.

Neuron - Functional Unit of the Nervous System:  The human nervous system is chiefly made of cells called neurons.  The nervous system is concerned with receiving the stimulus from the external and internal environment of the body and interpreting these stimuli.  To achieve this, specialised cells are used called neurons.  Neurons are the structural and functional unit of nervous system and are the largest cells found in the body.

Structure of Neuron: 

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Most neurons consist of three distinct regions- the cell body, dendrites and axon. Universal Tutorials – X CBSE (2012–13) – Biology

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The Cell Body: 



The cell body contains a well defined nucleus and nucleolus surrounded by a granular cytoplasm. Typical cell organelles like lysosomes, mitochondria, and Golgi complex are found within the cytoplasm.

Dendrites: 

These are short, usually highly branched extensions of the cytoplasm of the cell body. Their fine branching nature allows them to reach the remotest parts of the body from where they conduct nerve impulses towards the cell body.

Axon: 







It is usually a single long, thin process that is highly specialized and conducts nerve impulses away from the neuron or muscular glandular tissue. Many axons are surrounded by a white multi-layered sheath called myelin sheath. The myelin sheath increase the speed of nerve impulse and also insulates the axon, i.e., prevents the nerve impulse from mixing. Between the segments of the myelin sheath are unmyelinated gaps called Nodes of Ranvier. The functional junction between the neurons is called synapse.

Function of Neuron (Transmission of Nerve Impulse): 





 







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Neurons have the capability to carry messages. These messages travel along the neuron in the form of chemical and electrical signals. These chemical and electrical signals are nerve impulses. Nerve impulses are carried by dendrites towards cell body. Nerve impulse travels through axon and reaches synaptic knob of the axon. Nerve impulse causes synaptic vesicles present in the synaptic knob to move towards the synaptic knob membrane. Synaptic vesicles fuse with the synaptic knob membrane and then burst to release neurotransmitter substance in the synaptic gap. Neurotransmitter substance diffuses through the synaptic gap and initiates a nerve impulse in the dendrites of the adjacent neuron. In this way, neurotransmitter substance helps in the transmission of nerve impulse from axon of one neuron to dendrites of another neuron. The neurotransmitter substance is present only on the axon side at each synapse or junction. Therefore, nerve impulse can move in only one direction in the chain of neurons. Universal Tutorials – X CBSE (2012–13) – Biology

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Movement of Muscles Tissue:   



When nerve impulse reaches the muscles. Muscle cell change their shape. Because muscles cell is made up of special protein. Protein can change their shape and their arrangement in the cell in response to electrical impulses New arrangement of these proteins give the muscles cells a short form (contract).

Types of Neuron:  





Neurons are of three types: Sensory Neurons: Sensory neurons transmit nerve impulses from the sense organs to the central nervous system [brain and spinal cord]. Motor Neurons: Motor neurons transmit nerve impulses from the central nervous system [brain and spinal cord] to muscles and glands. Interneurons [Relay neurons]: Interneurons occur between the sensory neurons and motor neurons in the central nervous system [brain and spinal cord]. Interneurons pass [relay] nerve impulse from one neuron to another.

Components of Nervous System: 

Components of nervous system are central nervous system, peripheral nervous system.

Central Nervous System (CNS):  It consists of the brain and spinal cord.  They receive information from all parts of the body and integrate it

Brain: 

Brain is the highest coordinating centre in the body.  It is protected under brain box called cranium made up of bones.  Cerebrospinal fluid is a liquid present between the meninges that protects the brain from mechanical shocks.  Brain is broadly divided into three regions i.e. fore brain, mid brain and hind brain. Fore Brain:   

Fore brain is the main thinking part of brain Fore Brain consists of cerebrum and olfactory lobes, hypothalamus. Cerebrum is the most complex and specialized part of brain and has two cerebral hemispheres provided with sensory areas and motor areas which control the movement of voluntary muscles. [This space is left intentional for student to draw diagram]

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Olfactory lobes are concerned with the sense of smell. Hypothalamus it regulate the feeling of hunger

 

Mid Brain: Mid Brain have two optic lobes. The superior lobe acts as centres for visual reflexes. The inferior lobe acts as centres for auditory reflexes.

  

Hind Brain: It consists of three centres i.e. cerebellum, pons and medulla oblongata. Cerebellum controls the coordination and adjustment of movement and posture. It controls walking in a straight line riding a bicycle picking up a pencil. Pons regulates the rate of respiration. Medulla oblongata acts as a regulatory centre for swallowing, coughing, sneezing and vomiting and has cardiac and respiratory centres as well.

    

Spinal Cord: 

Spinal cord is a cylindrical cord like structure situated in the canal present in vertebral bones and is surrounded by menings.  It begins in continuation with medulla oblongata and extends downwards.  Spinal cord is a major centre of reflex activity. It reduces the burden for brain and allows the individual to deal with emergencies more effectively and spontaneously.  Spinal cord conducts and integrates both sensory and motor impulses to and from the brain.

Peripheral Nervous System (PNS): 

The peripheral nervous system is composed of the cranial nerves and the spinal nerves.  Cranial nerves originate from brain and spinal nerves originate from spinal cord. Note: Number of cranial nerves is 12 pairs. Total number of spinal nerves is 31 pairs.

Nervous System Peripheral Nervous System (PNS)

Central Nervous System (CNS): Brain

Spinal Cord

Voluntary / Somatic Nervous system

Fore Brain Cerebrum

Olfactory

Mid Brain Hypothalamus

Optic lobes

Superior lobe (visual reflexes)

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Involuntary / Autonomic Nervous system

Hind Brain Cerebellum

Pons

Medulla Oblongata

Inferior lobe (auditory reflexes)


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Reflex Action: Reflex: 

A reflex action is defined as a spontaneous, involuntary nervemediated activity produced by effectors at the unconscious level by stimulating specific receptors.  Reflex arc It is the path travelled by a nerve impulse from the region of stimulation (receptors) to the region of response (effectors i.e. muscles or glands).  It involves five structures i.e. receptor organ, afferent or sensory neuron, spinal cord, efferent or motor neuron and effectors.  Examples of reflex actions include knee-jerk reflex, coughing, sneezing, yawning, blinking of eyes, movement of the diaphragm etc  Reflex action is of two types:  Spinal reflex action: The reflex action controlled by spinal cord is called spinal reflex action.  Cerebral reflex action: The reflex action controlled by brain is called cerebral reflex action.  The importance of reflex action is given below:  Reflex action enables the human beings to respond immediately to the harmful stimuli.  Most of the reflex actions are spinal reflexes. Therefore, reflex gives relief to the brain.

Hormones:  Term hormone was introduced by Bayliss and Starling.  Hormones are chemicals, other than nutrients, which are generally synthesised in one part of the body and translocated to another part through circulatory system for triggering one or more physiological reactions even when present in very low concentration.  Hormones are produced by endocrine glands. Endocrine glands are the glands which do not have ducts to pass their secretion i.e. hormones. So they are called ductless glands.  Characteristics of a hormone are:  They are specific chemical messengers. They are secreted by endocrine glands.  They are poured directly into the blood and carried by blood circulation.  They act on specific tissue or organ called target organ.  Endocrine glands are located in different parts of the body.  Various endocrine glands in our body are hypothalamus, pituitary (hypophysis), pineal, thyroid, parathyroid, pancreas, adrenal, testis and ovary.  Hypothalamus is known as master of master gland. Hypophysis is known as master gland.  Some of the endocrine glands perform dual function and such glands are called heterocrine glands. For example, pancreas (secretes hormones as well as digestive enzymes), testis and ovaries (secretes hormones as well as gametes).  Hormones are involved in the regulation of several functions like growth, metabolic activities and reproduction.  Iodine is essential for the synthesis of thyroxin. In case iodine is deficient in our diet, there is a possibility that we might suffer from goitre. One of the symptoms in this disease is a swollen neck.

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Chapter 07: Control and Co–ordination Endocrine glands Hypothalamus Pituitary (hypophysis)

Hormones Releasing hormones Growth hormone

Trophic hormone

Thyroid

Prolactin Vasopressin Oxytocin Thyroxine

Parathyroid Adrenal

Calcitonin Parathormone Adrenalin and Corticoids

Pancreas

Insulin

Testes

Glucagon Testosterone

Ovary

Estrogen and Progesterone

125 Functions Regulation of the secretion of hormones from pituitary gland Development of bones and muscles. (If there is a deficiency of this hormone in childhood, it leads to dwarfism) Regulation of the secretion of hormones from endocrine gland, like adrenal, thyroid, testes and ovary Regulation of function of mammary gland Regulation of water and electrolyte balance Regulation of the ejection of milk during lactation Regulation of metabolism of carbohydrate, fat, and protein. (The deficiency of thyroxine hormone slows down growth and mental development in children. This is called cretinism) Regulation of blood calcium and phosphate Regulation of blood calcium and phosphate Regulation of blood pressure, heart rate, carbohydrate breathing rate (these hormones are secreted in small amount all the time. But they are secreted in large amount when a person is frightened) Lowering of blood glucose (deficiency of insulin hormone in the body causes a disease known as diabetes) Increase of blood glucose Regulation of male accessory sex organs and secondary sexual characters like moustache, beard and voice Regulation of female secondary sexual characters like mammary gland, hair pattern and voice. Maintenance of pregnancy

Endocrine Glands, their hormones and functions

Hormonal control by feedback Mechanism:  If the sugar levels in blood rise, they are detected by the cells of the pancreas which respond by producing more insulin.  As the blood sugar level falls, insulin secretion is reduced.  The complete coordinating in the human body is achieved by the nervous system and endocrine system working together.

Coordination in Plants:  In plants, the control system is not as elaborate as in animals.  They do not have structures comparable to neurons. But they do respond to light, touch, gravitational force and other stimuli.  Growth and movements in plants are regulated by both external and internal factors.  The function of control and coordination in plants is performed by chemical substances known as plant hormones or phytohormones or growth regulators.  The hormones are of different types namely auxins, gibberellins, cytokinins, abscisic acid and ethylene.  Auxins synthesized at the shoot tip, auxin helps the cells to grow longer. When light is coming from one side of the plant, auxins diffuses towards the shady side of the shoot. Volume


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 This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light, therefore plant bends towards light.  Gibberellins help in growth of the stem.  Cytokines promote cell division. It is present areas of rapid cell division such as in fruits and seeds.  Abscisic acid is inhibitor hormones. Therefore it inhibits growth its effects include witting of leaves  Ethylene helps in ripening of fruits.

Movements of Plant: 

Plants shows two different types of movement one dependent on growth and other independent of growth.

Tropism: 

The movement of the plant in the particular direction is known as tropism.  Various stimulus are light as seen in growing plant shoot (phototropism), gravitational force as seen in downward movement of roots (geotropism), chemical stimulus as seen during the pollen tube growth (chemotropism).  Hydrotropism: The movement of a part of the plant is response to water is called hydrotropism.

Nastic Movement: 

Movements, which take place with a response to any stimulus, are the nastic movements as is seen in sensitive plant ‘touch-me-not’, the movement is neither towards nor away from the stimulus.  The synthesis and action of phytohormones is controlled by the presence of external stimuli.  The nastic movement is not a directional movement of a plant part with respect to stimulus  The movement happens at a point different from the point of touch. So, information that a touch has occurred must be communicated.  The plants also use electrical-chemical means to convey this information from cell to cell, but unlike in animals, there is no specialised tissue in plants for the conduction of information. The change in shape of the cell takes place so that movement occurs.  Instead of the specialised proteins found in animal muscle cells, plant cells change shape by changing the amount of water in them, resulting in swelling or shrinking, and therefore in changing shapes.  The main difference between the tropic movement and nastic movement is:  Tropic movement is directional movement of a plant part with respect to stimulus.  Nastic movement is not a directional movement of a plant part with respect to stimulus. APPENDIX:

Activity 7.1: Put some sugar in your mouth. How does it taste? Block your nose by pressing it between your thumb and index finger. Now eat sugar again. Is there any difference in its taste? While eating lunch, block your nose in the same way and notice if you can fully appreciate the taste of the food you are eating.

126

Sweat No

Yes


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127

Activity 7.2: Have the old parts of the shoot and root changed direction? Are there differences in the direction of the new growth? What can we conclude from this activity?

No Yes Growing part of plants show response to the external stimulus.

Activity 7.3: Identify the endocrine glands mentioned in the figure. Some of these glands have been discussed in the text. Consult books in the library and discuss with your teachers to find out about the functions of other glands.

Hypothalamus, pituitary, pineal, thyroid parathyroid, pancreas, adrenal, tastes, ovar Refer table of endocrine gland

NCERT EXERCISE: 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14) 15) 16) 17) 18) 19) 20) 21) 22) 23) 24)

What is the difference between a reflex action and walking? What happens at the synapse between two neurons? Which part of the brain maintains posture and equilibrium of the body? How do we detect the smell of an agarbatti (incense stick)? What is the role of the brain in reflex action? What are plant hormones How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light? Give an example of a plant hormone that promotes growth. How do auxins promote the growth of a tendril around a support? Design an experiment to demonstrate hydrotropism. How does chemical coordination take place in animals? Why is the use of iodised salt advisable? [2008] How does our body respond when adrenaline is secreted into the blood? Why are some patients of diabetes treated by giving injections of insulin? What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise? Draw the structure of a neuron and explain its function. How does phototropism occur in plants? Which signals will get disrupted in case of a spinal cord injury? How does chemical coordination occur in plants? What is the need for a system of control and coordination in an organism? How are involuntary actions and reflex actions different from each other? Compare and contrast nervous and hormonal mechanisms for control and coordination in animals. [2005] What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs? Multiple Choice Questions: i) Which of the following is a plant hormone? a) Insulin b) Thyroxin c) Oestrogen d) Cytokinin

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ii) The gap between two neurons is called a a) dendrite b) synapse c) axon d) impulse iii) The brain is responsible for a) thinking b) regulating the heart beat c) balancing the body d) all of the above PREVIOUS BOARD QUESTIONS: Very Short Answer type Question: [1 Mark] 1) Name two tissues that provide control and co–ordination in multicellular animals. 2) Name the largest cell present in the human body 3) What is a neuron? 4) What are phytohormones? 5) Write the function of hormone ‘thyroxin’ in our bodies. Short Answer type Question: [2 Marks] 6) What are “Nastic” and “Curvature” movements? Give one example of each. 7) Explain ‘reflex action’ with a suitable example. 8) Name the two hormones secreted by pancreas and write one function of each. 9) What are the main divisions of the nervous system? 10) Differentiate between tropic and nastic movements in plants. Give one example of each. 11) Write any two functions of pancreas. 12)

[2009] [2008] [2007] [2007] [2004] [2009] [2007] [2007] [2006] [2006] [2005]

[2004]

i) Label the two parts indicated by question marks. ii) Suggest a suitable heading for the diagram. Short Answer type Question: [3 Marks] 13) What is phototropism? How does it occur in plants? Describe the activity to demonstrate phototropism. [2009] 14) Define ‘hormone’. Name the hormone secreted by thyroid. Write its function. Why is the use of iodised salt advised to us? [2008] 15) Differentiate between endocrine gland and exocrine gland. [2006] 16) Define nerve impulse’. Which structure in a neuron helps to conduct a nerve impulse i) towards the cell body ii) away from the cell body [2004] Long Answer type Question: [5 Marks] 17) a) Draw the structure of a neuron and label the following on it: [2008] Nucleus, Dendrite, Cell body and Axon b) Name the part of neuron: i) where information is acquired ii) through which information travels as an electrical impulse. 18) a) What is (i) phototropism and (ii) geotropism? With labeled diagrams describe an activity to show that light and gravity change the direction that plant parts grow in. b) Mention the role of each of the following plant hormones: i) Auxin ii) Abscisic Acid [2008] 128


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19) a) What is a reflex action? Give its two examples. Illustrate the pathway followed by a message from the receptor in a reflex arc. b) Name the sympathetic and para–sympathetic systems of eye. [2006] 20) a) What are ‘hormones’? [2006] b) List four characteristics of hormones c) Name the hormone required for the following: i) Functioning of mammary glands ii) Regulation of calcium and phosphate in blood iii) Lowering of blood glucose iv) Development of moustaches and beard in human male. MISCELLANEOUS EXERCISE: Very Short Answers: 1 Mark 1) Name the source glands of prolactin and estrogen. 2) Name any two types of tropism? 3) What is the response of plants to light? 4) What are two systems which control and coordinate the various body systems? 5) List any four plant hormones. 6) Define phototropism and chemotropism. 7) Name the parts of brain which function as endocrine glands. 8) Name the part of the brain which is concerned with regulation of respiration. 9) Which part of nervous system controls involuntary muscles? 10) Name the male and female sex – hormones. 11) We suddenly withdraw our hand when a pin pricks. Name the type of response involved in this action. 12) A particular hormone which if deficient leads to diabetes mellitus. Name the hormone and where is it produced. 13) In Circus we see jokers who are dwarfs. This dwarfism is caused due to certain hormone. Name the hormone. Where is the endocrine gland situated which secretes this particular hormone? 14) Alisha hears shocking news about the plane crash and reacts suddenly. Which hormone prepares the body to meet this emergency situation? Where is the endocrine gland which secretes the above hormone located in the human body? 15) What is stimulus? 16) What are receptors? 17) What is reflex arc? 18) What is the importance of reflex actions? 19) What are the membranes covering the brain? 20) What are nastic movements? 21) What is synapse? 22) Name the hormone which induces milk secretion. 23) Name the hormone which controls the development of secondary sexual characters in females. 24) Define nervous system. 25) What is nerve impulse? 26) What are the functions of cerebellum? 27) Give two functions of spinal cord. 28) Write the functions of any one part of hind brain. 29) What is the autonomic nervous system? 30) What is the function of nervous system? 31) Name the following: a) Structural and functional units of the nervous system. Volume


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b) c) d) e)

Two types of peripheral nerves. Most important part of the nervous system. Three divisions of human brain. The part of brain concerned with the regulation of skeletal muscular activities and postural mechanism. f) The part of the brain associated with intelligence, sight, hearing and speech. g) The hormone which prepares the body to meet any emergency situation. h) Type of nerve which conducts the impulses from the various organs to the central nervous system. i) Response to stimulus without the intervention of the will of an animal. j) The part of the brain which is concerned with memory. k) The gland which functions both as exocrine and endocrine gland. l) The gland which is called ‘Master gland’ m) The two hormones secreted by pituitary body. n) The hormone associated with lactation in mammals. o) The hormone secreted by thyroid gland. p) The hormone secreted by parathyroid gland. q) The hormones that control blood glucose level. r) The endocrine gland located on the top of kidneys. s) The gland which secretes insulin. Short Answers: 2 – 3 Marks 32) Name the gland that secretes vasopressin. What are its two principal actions? 33) Name the two hormones released from the thyroid and explain their functions. 34) Give the names and functions of hormones secreted by pituitary gland. 35) Mention the functions of the fore brain. 36) List the components of nervous system. 37) What parts of the brain are located in each basic region? 38) What do you understand by the following: i) Voluntary action ii) Reflex action iii) Reflex arc iv) motor neuron and v) sensory neuron 39) Name and locate six endocrine glands. 40) What are growth regulators? 41) Trace the events occurring in a reflex action as sneezing. 42) Write a note on Spinal cord. 43) What are endocrine or ductless glands? Give the position of different endocrine glands in the body of human beings. 44) Name the hormones secreted by thyroid, parathyroid and pancreas. 45) List the functions of testosterone and estrogen. 46) Nervous and hormonal system together performs the function of control and coordination in human beings. Justify the statement. 47) List some of the functions of adrenal glands. 48) What is nervous tissue made up of and what is its function? 49) What are the functions of medulla oblongata? Long Answers: 5 Marks 50) Draw a labelled diagram showing a nerve cell with an axon terminating in the neuromuscular junction. 51) Describe the central nervous system in human beings. 52) Write a note on coordination in plants. 53) How nerve impulses travel in the body? 54) Explain Human brain in detail. 130


Volume

Chapter 12: Electricity

131

Chapter 12: Electricity Chapter Map: → Introduction → Classification of substances → Current Electricity ↓ Electric current

↓ Units

→ P.D. and Electric potential ↓ ↓ Definition Units → Electric Circuits → Ohm’s Law ↓ Statement

↓ Verification

→ Resistance ↓ ↓ Concept Law of Resistance → Methods of Joining Resistances ↓ ↓ ↓ Series Parallel Combination of series and parallel → Heating effect ↓ ↓ Joule’s Law Applications → Electric Power

Introduction:  Electricity is a form of energy, which can be easily converted to other forms and can be easily transmitted to large distances. It is a convenient and controllable form of energy.  Types of electricity: (i) Static Electricity (ii) Current Electricity.  Static electricity: Static electricity is due to electric charges at rest.  Electric charges are of two types: negative charge and positive charge.  Static electricity is also called frictional electricity as it can be produced by rubbing two suitable bodies together. One of the bodies loses some electrons and the other gains the same. Hence, both the bodies get charged equally but opposite in nature.  eg. when a glass rod is rubbed with silk, glass acquires positive charge and silk acquires negative charge as glass loses electron to silk.  Like charges repel and unlike charges attract.

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Current Electricity:  Electric current in a metallic conductor is the flow of electrons in it in a given direction.  Each electron has a negative charge of 1.6 × 10

–19

Coulombs.

 1 Coulomb = 6.25 × 10 electron charges.  The strength of current in a conductor is defined as the rate of flow of charge through a particular area of the conductor. 18

 Current =

ch arg e time

 If Q is the charge flowing in time ‘t’, then the current, I =

Q . t

Unit: 

SI unit of current is ampere (A). 1 ampere =

1coulomb (C) 1second (s )

Definition: 

The current is said to be 1 ampere if a charge of one coulomb flows past a certain area of a 18 conductor in 1 second. If 6 × 10 electrons flow through a conductor in 1 s, the current is 1A.

Note: One of the earliest devices which produced a source of steady current is the Voltaic Cell. 

The conventional direction of current is from positive to negative terminal of the source. An ammeter is used to measure current in a circuit.  It is always connected in series with the source / appliance in a circuit. 

Classification of Substances: Conductors: 

They are materials which allow electric current through them readily. Eg. metals, acidified water, graphite etc.  Solid conductors have large number of free electrons; liquid conductors have free ions.  Copper and aluminium are used for electrical transmission lines as they are good conductors of electricity and economically viable.

Insulators: 

They are materials which do not allow current to flow through them eg. rubber, paper, wood.

Electric Potential and Potential Difference:  Electric Potential at a point is defined as, the work done in bringing a unit charge from infinity to that point.  Electrons will move along a wire only if there is a difference in potential between two points in the conductor.  This difference in potential is provided by a suitable source (cells, generators etc.)  Work has to be done for the electrons to move from one point to another in a conductor. 132


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 The electric potential difference between two points is the work done to move a unit charge from one point to the other. P.D =

Work done Charge

Unit: 

volt (V)

1 volt (V) =

1 joule 1coulomb

 1J    1C 

Definition: 

The potential difference between two points in a circuit is said to be 1 volt if 1 joule of work is done in moving 1 coulomb of charge from one point to the other.  In case of cells, the potential difference is set up by the chemical action, inside the cell even when no current is drawn. When the terminals are connected by a wire, the P.D. makes the electrons move through the wire.  P.D. is measured by a voltmeter. It is connected in parallel across the points between which P.D. is measured.

Electric Circuits:  A continuous and closed path for electric current is called electric circuit  A source of electricity, a key and a load with connecting wires constitute a circuit.  For current to flow, the circuit has to be complete (closed).

Symbols of some components: Component

Symbol

An electric cell Provide flow of charges Battery of cells Plug Key and switch or tap key (open)

and

A closed plug key or switch / tap key

and

A wire joint

(breaks the circuit) (makes the circuit)

(Form a conducting, link between cell and device)

Wires crossing Electric bulb (load) (opposes the current flow)

A resistance Rheostat and Variable resistance

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and


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134

Ammeter

A

Voltmeter

V

Galvanometer

G

A Simple circuit Diagram:

I

A

Key

Ohm’s Law:  It gives the relation between current in a metallic conductor and the potential difference across its ends.

Ohm’s Law: 

Electric current flowing through a metallic conductor is directly proportional to the p.d. across its ends, the temperature remaining constant. IαV ∴ V = IR Where R is the constant of proportionality called as resistance of the conductor.

Verification of Ohm’s Law:  When a graph of current through a conductor and the potential difference across its ends is plotted and if a straight line is obtained as in the figure then the conductor obeys Ohm’s law. Such conductors are called ohmic v conductors / resistors.  The slope of this graph gives the resistance.  R=

I

V I

Resistance:    

Symbol: R It is the property of a conductor to resist the current in it. It is the opposition offered to the flow of current in a conductor. The current through a resistor is inversely proportional to the resistance (eg. If resistance is doubled, current is halved) for a given voltage.

 Unit: The unit of resistance is ohm (Ω)  The resistance of a conductor is 1 ohm, if a potential difference of 1 volt is applied across its ends, causing a current of 1 ampere to flow through it.  Formula: Resistance = 134

p.d. v or R = current I


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135

1 ohm =

1V 1A

Concept of Resistance:  Conductors have free electrons that are in a state of random motion.  When pd is applied at its ends, free electrons begin to move in an orderly fashion from –ve to +ve terminal (current from +ve to –ve).  This constitutes electric current in the conductor.  But when electrons move, they collide with the atoms of the conductor.  These collisions oppose the orderly motion of electrons.  This opposition is called the resistance of the conductor.

Laws of resistance (factors on which resistance depends): 

The resistance of a conductor is directly proportional to the length of the conductor for a given area of cross section, at a given temperature.

Rαl ––––– (1)  The resistance of a conductor is inversely proportional to the area of cross section of the conductor for a given length, at a given temperature. Rα

1 A

Hence R = ρ

––––– (2)

l A

[where ρ is the constant of proportionality known as resistivity or

specific resistance of the material of the conductor]  The resistance of a wire also depends on the nature of the material.  Resistivity of a material is defined as the resistance across the ends of a conductor (of that 2 material) of length one meter and cross sectional area, 1 m . Unit of ρ is ohm meter (Ωm)  Resistivity depends on the material and temperature. Metals and alloys have low resistivity (10 to 10 Ωm) but insulators have high resistivity 12 17 (10 to 10 Ωm).  As resistivity of alloys is more than that of metals and they do not oxidize easily, they are used as heating elements. –8



–6

Resistivity of some common substances at 20° C: Materials Conductor

Volume

Silver Copper Aluminium Tungsten Nickel Iron Chromium Mercury Manganese

Resistivity (ohm m) –8 1.60 × 10 –8 1.62 × 10 –8 2.63 × 10 –8 5.20 × 10 –8 6.84 × 10 –8 10.0 × 10 –8 12.9 × 10 –8 94.0 × 10 –6 1.84 × 10


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Alloys

Constantan (alloy of Cu and Ni) Manganin (alloy Cu, Mn and Ni) Nichrome (alloy of Ni, Mn, Fe and Cr) Glass Hard rubber Ebonite Diamond Paper (dry)

Insulators

49 × 10 –6 44 × 10 –6 100 × 10 10 14 10 – 10 13 16 10 – 10 15 17 10 – 10 12 13 10 – 10 12 10 –6

Methods of joining Resistors: Resistors in Series:  When a number of resistors are connected end to end such that the current has only one path to follow, the resistors are said to be connected in series.  Let three resistances R1, R2, and R3 be connected in series between X and Y.  Let v1 be the potential difference across R1, v2 across R2 and v3 across R3.  Total pd (v) across XY = v1 + v2 + v3 v3 v2 v1  According to Ohm’s law: v = IR ∴ v1 = IR1; v2 = IR2; v3 = IR3 Where I is the current.  If Rs is the effective resistance, then:

X

I

R1

F

Q

R2

T

S

R3

Y I

K

A IRs = IR1 + IR2 + IR3 v IRs = I(R1 + R2 + R3) Rs = R 1 + R2 + R3  Thus equivalent (effective) resistance in series is the sum of the individual resistances.  RS is greater than individual resistances.

Resistors in Parallel:  When a number of resistors are connected between two common points so that the potential difference across each of the resistors is the same, the combination is called a parallel combination of the resistors.  Three resistors R1, R2, and R3 are connected in parallel between two common points X and Y. Thus the potential difference across each of the resistances is the same.  Let I1, I2 and I3 be the current through R1, R2, R3 respectively.  Let Rp be the effective resistance across XY.  As current gets distributed, I = I1 + I2 + I3 V V V V  According to Ohm’s law, I1 = , I2 = , I3 = and I = R1 R2 R3 Rp R1  Substituting for I = I1 + I2 + I3, we get, I1 L M R2 V V V V X I2 Y = + + I3 P Q R1 R 2 R3 Rp R3 ∴

1 1 1 1 = + + R1 R2 R3 Rp

S I

T V

V

I

K A

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 The reciprocal of equivalent resistance is the sum of reciprocals of individual resistances when resistors are connected in parallel.  Rp is less than individual resistance.



Why household wiring is done in parallel?

Ans: It is obviously impracticable to connect an electric bulb and an electric heater in series, because they need currents of widely different values to operate properly. Another major disadvantage of a series circuit is that when one component fails the circuit is broken and none of the components work. A parallel circuit divides the current through the electrical gadgets. The total resistance in a parallel circuit is decreased. Parallel connection is helpful particularly when each gadget has different resistance and requires different current to operate properly. Also each branch of the household circuit can be control individually in parallel connection.

Heating Effect of Electric Current:  When current flows through a resistor, the wire gets heated. This is because of the resistance offered by the conductor  The electrical energy gets converted to heat energy.  This is heating effect of current.  Experimentally it was proved that heat produced in a conductor by an electric current increases if,  potential difference across the coil is increased,  current passing through the coil is increased and  time for which the current flows is increased.

Joule’s law for heating effect of electric current:  Consider a current I flowing through a resistor of resistance R. Let the potential difference across it be v. Let t be the time during which a charge Q flows across. The work done in moving the charge Q through a potential difference v is vQ. Therefore, the source must supply energy equal to vQ in time t. Hence the power input to the circuit by the source is P=v

Q = vI t

 The energy supplied to the circuit by the source in time t is P × t, i.e. vIt. This energy gets dissipated in the resistor as heat. Thus for a steady current I, the amount of heat H produced in time t is: H = v⋅I⋅t = I ⋅R⋅t 2

v ⋅t R 2

=

[since v = IR] [since I =

v ] R

H = I ⋅R⋅t is the mathematical expression for Joule’s law of heating. 2

Joule’s law: 

The quantity of heat (H) generated in a conductor, when a current flows through the conductor for a given time is directly proportional to  the square of the current  the resistance of the conductor and  the time for which the current flows.  The heat generated is in joules if current is in ampere, resistance in ohm and time in second. Volume


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 Since 4.18 J = 1 calorie,

I2Rt v 2t v 2t calorie or H = joule = calorie 4.18 R 4.18 R where v is the potential difference across the conductor expressed in volt. H = I Rt joule = 2

Applications of heating effect of current:  Electric bulbs, heaters, geysers, electric stoves, electric iron, fuse wire etc work on heating effects of current.  Almost all electrical energy is converted to heat energy.

Electric bulb:  It consists of a coiled tungsten filament in glass bulb filled with inactive nitrogen and argon to prolong the life of the filament.  Tungsten has high resistivity and high melting point (3380° C).  When a current flows through the filament, it gets heated to a high temperature or produces light. This phenomena is called incandescence.

Electric Fuse:  When a short circuit occurs the resistance decreases and hence current increases in the circuit.  As current increases, large amount of heat is produced and it may cause fires.  An electric fuse is a safety device used to protect electrical appliances from damage due to high current.  A fuse wire is made of a material of low melting point and resistance appropriate for the rated value of current in the circuit. Contact  The fuse is connected in the phase wire and in series with the appliance.  When a high current (above the rated value) flows through a circuit, the fuse wire melts and breaks the circuit. Thus, the appliances in the circuit are saved from damages.  Fuses are of two types: Fuse wire  Fuse wire in a glass tube.  Fuse wire in a porcelain case. Contacts  Generally fuses are rated as 1A, 2A, 3A, 5A, 10A. Glass tube  Good fuse wires are made of aluminium, copper iron and lead.  Common fuse wires are made of an alloy of tin and lead.

Electric Power: Definitions:  The rate at which electric energy is dissipated or consumed is electric power.

Power (P) = 

138

work( w ) 2 = I R or vI time( t )

Unit: SI unit of power is watt (W)

1 watt is the power generated when one joule of work is done (1 joule of energy is consumed) per second. Universal Tutorials – X CBSE (2012–13) – Physics

Volume


1W =

1J 1s

139

CGS unit: erg/ second.

Useful Conversions:      

1 watt (W) = 1 joule/ second 3 1 kilowatt (kW) = 10 watts 6 1 megawatt (MW) = 10 watts 1 horse power (hp)= 746 watts 7 1 watt = 10 erg/second The commercial unit of electrical energy is kilowatt hour (kWh) 

1kWh = 1000W × 3600 s

1kWh = 3.6 × 10 joule 6

Hints to solve the numerical: 1) If resistors are connected in series, current (I) remains the same through each resistor and its value is equal to the total current in the circuit. Hence the p.d. across each resistor is given by the formula v = IR. 2) If resistor are in parallel, p.d. (v) is same across each resistor and it is equal to total voltage v applied to the circuit. Hence the current (I) in each resistor is given by the formula I = . R 3) If internal resistance of a cell is given, then total resistance (R) in series is given by R = R1 + r v where R1 is the resistor and r is internal resistance. Then current I = . R1 + r APPENDIX: Activity 12.1 (Experiment): Aim: To verify Ohm’s Law Apparatus: Nichrome Wire, ammeter, Voltmeter, Four cells Procedure: Step 1)

2)

3)

4) 5)

6) Volume

Set up a circuit as shown in Fig., consisting of a nichrome wire XY of length, say 0.5 m, an ammeter, a voltmeter and four cells of 1.5 V each. (Nichrome is an alloy of nickel, chromium, manganese, and iron metals.) First use only one cell as the source in the circuit. Note the reading in the ammeter I, for the current and reading of the voltmeter V for the potential difference across the nichrome wire XY in the circuit. Tabulate them in a Table column. Next connect two cells in the circuit and note the respective readings of the ammeter and voltmeter for the values of current through the nichrome wire and potential difference across the nichrome wire. Repeat the above steps using three cells and then four cells in the circuit separately. Calculate the ratio of V to I for each pair of potential difference V and current I. Plot a graph between V and I, and observe the nature of the graph. Universal Tutorials – X CBSE (2012–13) – Physics

Reason / Observation ––

––

–– ––

V I is constant It is a straight line The ratio

139

140

Conclusion: Graph of V and I is a straight line and V = constant, R. ratio I

V

X

V

R

V V

Y

V Activity 12.2 (Experiment): Aim: To find the current through different resistors Apparatus: Battery, key, ammeter, nichrome wire, 10W bulb and torch bulb Procedure: Step

K A

Reason / Observation

1)

Take a nichrome wire, a torch bulb, a 10 W bulb and an ammeter (0 – 5 A range), a plug key and some connecting wires.

––

2)

Set up the circuit by connecting four dry cells of 1.5 V each in series with the ammeter leaving a gap XY in the circuit, as shown in Fig.

––

3)

Complete the circuit by connecting the nichrome wire in the gap XY. Plug the key. Note down the ammeter reading. Take out the key from the plug. [Note: Always take out the key from the plug after measuring the current through the circuit.]

Resistance increases with temperature

4)

Replace the nichrome wire with the torch bulb in the circuit and find the current through it by measuring the reading of the ammeter.

––

5)

Now repeat the above step with the 10 W bulb in the gap XY.

––

6)

Are the ammeter readings different for different components connected in the gap XY? What do the above observations indicate?

Yes

7)

You may repeat this Activity by keeping any material component in the gap. Observe the ammeter readings in each case. Analyse the –– observations. Conclusion: The ammeter reading is different because different components offer different resistance. A X

Y

K

I

Nichrome wire

10 W bulb

Torch bulb

Activity 12.3: Complete an electric circuit consisting of a cell, an ammeter, a nichrome wire of length l [say, marked 1] and a plug key, as shown in Fig. Now, plug the key. Note the current in the ammeter. Replace the nichrome wire by another nichrome wire of same thickness but twice the length, that is 2l [marked (2) in the Fig.]. Note the ammeter reading. Now replace the wire by a thicker nichrome wire, of the same lengthl [marked (3)]. A thicker wire has a larger cross-sectional area. Again note down the current through the circuit. Instead of taking a nichrome wire, connect a copper wire [marked (4) in Fig.] in the circuit. Let the wire be of the same length and same area of cross-section as that of the first nichrome wire [marked (1)]. Note the value of the current. Notice the difference in the current in all cases. 140


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Does the current depend on the length of the conductor? Does the current depend on the area of cross-section of the wire used? Ans: Yes, Current depends on the length and area of cross section of the wire because Resistance depends on its length, area of cross–section and nature of material. Activity 12.4: Join three resistors of different values in series. Connect them with a battery, an ammeter and a plug key, as shown in Fig. You may use the resistors of values like Ω, 1 2Ω, 3 Ω etc., and a battery of 6 V for performing this Activity. Plug the key. Note the ammeter reading. Change the position of ammeter to anywhere in between the resistors. Note the ammeter reading each time. Do you find any change in the value of current through the ammeter? Ans: No, In series the current remains same. Activity 12.5 (Experiment): Aim: To find the voltage across each resistor in series Apparatus: Three resistance, ammeter, voltmeters, Battery and key. Procedure: Step


1)

In Activity 12.4, insert a voltmeter across the ends X and Y of the series combination of three resistors, as shown in Fig.

––

2)

Plug the key in the circuit and note the voltmeter reading. It gives the potential difference across the series combination of resistors. Let it be V. Now measure the potential difference across the two terminals of the battery. Compare the two values.

––

3)

Take out the plug key and disconnect the voltmeter. Now insert the voltmeter across the ends X and P of the first resistor, as shown in Fig.

––

4)

Plug the key and measure the potential difference across the first resistor. Let it be V1.

––

5)

Similarly, measure the potential difference across the other two resistors, separately. Let these values be V2 and V3, respectively.

––

6) Deduce a relationship between V, V1, V2 and V3. V=V1+V2+V3 Conclusion: V = V1 + V2 + V3. In series the p.d. gets distributed between the resistors.

Activity 12.5: Make a parallel combination, XY, of three resistors having resistances R1, R2, and R3, respectively. Connect it with a battery, a plug key and an ammeter, as shown in Fig. Also connect a voltmeter in parallel with the combination of resistors. Volume


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Plug the key and note the ammeter reading. Let the current be I. Also take the voltmeter reading. It gives the potential difference V, across the combination. The potential difference across each resistor is also V. This can be checked by connecting the voltmeter across each individual resistor (see Fig. 12.11). Take out the plug from the key. Remove the ammeter and voltmeter from the circuit. Insert the ammeter in series with the resistor R1. Note the ammeter reading, I1. Similarly, measure the currents through R2 and R3. Let these be I2 and I3, respectively. What is the relationship between I, I1, I2 and I3?

Conclusion: In parallel circuit the current gets distributed across the resistors. I = I1 + I2 + I3 SOLVED EXAMPLES:

Ohm’s Law:



The resistance of a heater is 25Ω. It is connected to 90V source. Find the current drawn.

Sol:

V = 90V

 Sol:



R = 25Ω

I=?

I=

V R

∴ I = 90 = 3.6A 25

What is the resistance of a conductor if it takes 5A current when connected to 220V source? V 220 V = 220V I = 5A R=? R= = = 44Ω I 5

Sol:

An electric lamp of 88Ω takes a current of 2.5A. What is the voltage required to work? R = 88Ω I = 2.5A V =? V = IR = 88 × 2.5 = 220V

Sol:

How many electrons are there in 1 coulomb of charge? 18 6.25 × 10 electrons

  Sol:

 Sol:

What is the resistance of a hot electric arc lamp, if the lamp uses 20A when connected to 220V line? V = IR R = 220 = 11Ω 20 A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the amount of electric charge that flows through the circuit. We are given, I = 0.5 A; t = 10 min = 600 s. Q = It = 0.5 A × 600 s = 300 C



a) How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb filament is 1200Ω? b) How much current will an electric heater coil draw from a 220 V source, if the resistance of the heater coil is 100Ω? Sol: a) V = 220 V; R = 1200Ω. I = 220 V/1200Ω = 0.18 A. b) V = 220 V, R = 100Ω. I = 220 V/100Ω = 2.2 A.

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Note the difference of current drawn by an electric bulb and an electric heater from the same 220 V source.

Resistances:

 Three resistance 1Ω, 2Ω, 3Ω are connected in series. What is the total resistance? Sol: In series R = R1 + R2 + R3 R3 = 3Ω ⇒ R = 1 + 2 + 3 = 6Ω

R1 = 1Ω, R2 = 2Ω,

 Two resistances 6Ω and 3Ω are connected in parallel. What is the equivalent resistance? Q

Sol: In parallel, 1 = 1 + 1 R R1 R2

1 = 1+1= 3 R 6 3 6



R1 = 6Ω

R2 = 3Ω

1Ω

B P

R= 6 = 2Ω 3

or

1Ω

A R

2Ω

2Ω S

A 4 Ω resistance wire is doubled on it. Calculate the new resistance of the wire.

Sol: R = 4Ω. When a wire is doubled on it, its length would become half and area of cross-section would double. That is, a wire of length l and area of cross-section A becomes of length l/2 and area of cross–section 2A. R=ρ

l A

Therefore,

R1 = ρ

(l / 2) (2A )

R1 l 1 (l / 2) = ρ /ρ = R A 4 (2A )

where R1 is the new resistance. or

R1 =

R 4Ω = = 1Ω 4 4

The new resistance of the wire is 1Ω.

 Find the equivalent resistance between A and B. Sol: a) PQ and QR are in series and b) PS and SR are in series Equivalent diagram is

Q

2Ω

P

4Ω

1Ω

b) R2 = 2 + 2 = 4Ω

The combination is in parallel

∴ 1 = 1+ 1 = 2+1 ⇒R= 4Ω R 2 4 4 3

 What is the resistance between x and y

2Ω

2Ω

2Ω 2Ω

Sol: The equivalent diagram

2Ω

3Ω

X

Y

R2 = 3Ω

1 = 1 + 1 ⇒ 1 = 3 or R = 6 = 2Ω R 6 3 R 6 3

2Ω

2Ω

2Ω

3Ω

X

Y

 Find the resistance between A and B in the given figure. Sol: a) 10Ω + 10Ω = 20Ω

[Series]

20Ω A 10Ω

b) 20Ω, 20Ω are in parallel

B 10Ω

A 10Ω Volume

B R

S

a) R1 = 1 + 1 = 2Ω

R1 = 2 + 2 + 2 = 6Ω

1Ω

A

OR


10Ω

10Ω B 143

144

1 = 1 + 1 ⇒ R = 20 = 10Ω R 20 20 2 c) R = 10 + 10 = 20Ω

 Find the equivalent resistance between C and D Sol: 30Ω and 30Ω are in series

∴ 30 + 30 = 60Ω 30Ω

60Ω and 30Ω are in parallel ∴ 1 = 1 + 1 = 3 R 60 30 60

∴ R = 60 = 20Ω 3

C

30Ω 30Ω

D

Potential difference and EMF:

 Three resistors of 6Ω, 3Ω and 2Ω are connected in parallel. The combination of the above resistors is connected in series to a resistance of 4Ω and then to a cell of e.m.f. 1.5V. The internal resistance of cell is negligible. a) Draw the circuit diagram b) Calculate the current in main circuit c) Find the current in each of the resistor in parallel. E=1.5v Sol: a) 6Ω 3Ω

4Ω

2Ω

b)

Equivalent resistance of parallel combination R1 = 1 + 1 + 1 = 1 + 2 + 3 = 6 = 1Ω 6 3 2 6 6 Total resistance of the circuit = R = R1 + 4 ∴ R = 5Ω

c)

I = V = 1.5 = 0.3A R 5

V across parallel is I × R1 = 0.3 × 1 = 0.3V ∴ Current in 6Ω = 0.3 = 0.05A 6

∴ Current in 3Ω = 0.3 = 0.1A 3

∴ Current in 2Ω = 0.3 = 0.15A 2

 A cell of e.m.f. 1.5V records a p.d. of 1.2V, when connected to an external resistance R, such that current flowing through circuit is 0.5A. Calculate the value of R and internal resistance of the cell. Sol: E = 1.5V, V = 1.2V I= V R I=

E R+r

1.2 + 0.5r = 1.5

144

I = 0.5A, R = ? ∴ R = 1.2 = 2.4Ω 0 .5 ∴ 0.5 (2.4 + r) = 1.5 ⇒ r = 1.5 − 1.2 = 0.6Ω 0 .5


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

How much work is done in moving a charge of 2 C across two points having a potential difference 12 V? Sol: The amount of charge Q, that flows between two points at potential difference V (= 12 V) is 2 C. Thus, the amount of work W, done in moving the charge is W = VQ = 12 V × 2 C = 24 J.

Heating effect and power:

 An electric heater draws a current of 5A and its element has a resistance of 50Ω. If heater is switched on for 5 minutes, calculate the energy dissipated in kilojoules. Sol: I = 5A

R = 50Ω

t = 5min = 5 × 60secs

H = I Rt = (5) × 50 × 60 × 5 = 375000 J 2

2

or

375 KJ

 Calculate the total power of 5 fans, if each of them draws a current of 0.8A at p.d. of 220 V Sol: I = 0.8A

V = 220 V

P = VI = 0.8 × 220 Power of 1 fan = 176 W

∴ Power of 5 fans = 5 × 176 = 880 W

 Calculate the monthly bill for a heater of resistance 40 Ω, which is used on 220 V main such that its daily use is 5hr. The energy costs Rs.1.80per kW h

V 2 (220 ) = R 40

2

Sol: P =

= 1210 W

Energy consumed in 1 day = P × t = 1210 × 5 = 6050 W h Energy consumed in 30 days = 6050 × 30 = 181500 W h = 181.5 kW h Monthly Bill =



181.5 kW h × Rs.1.80 = Rs.326.70 kW h

An electric iron consumes energy at a rate of 840 W when heating is at the maximum rate and 360 W when the heating is at the minimum. The voltage is 220 V. What are the current and the resistance in each case?

Sol: We know that the power input is P = V I Thus the current I =

P V

a) When heating is at the maximum rate, I =

840 W = 3.82 A; 220 V

and the resistance of the electric iron is R =

V 220 V = = 57.60 Ω. I 3.82A

b) When heating is at the minimum rate, I =

360W = 1.64 A; 220 V

and the resistance of the electric iron is R =

V 220 V = = 134.15 Ω. I 1.64A

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

An electric refrigerator rated 400 W operates 8 hour/day. What is the cost of the energy to operate it for 30 days at Rs.3.00 per kW h? Sol: The total energy consumed by the refrigerator in 30 days would be 400 W × 8.0 hour/day × 30 days = 96000 W h = 96 kW h Thus the cost of energy to operate the refrigerator for 30 days is 96 kW h × Rs.3.00 per kW h = Rs.288.00 REVIEW QUESTIONS:

CW Exercise: (Theory) Very Short Answer Questions: 1 Mark 1) What do the following symbols represent?

(a)

(b)

(c)

2) A graph of V – I is shown. Which of them represents a metal? a)

I

b)

I

c)

I

V

V 3) Define Power and Watt V 4) Read the following statements. Write true or false against each: i) The quantity of charge flowing past a point multiplied by the time gives the current. ii) The flow of charge through a conducting wire connected to a cell is due to the chemical reaction inside the cell. iii) The resistivity of all pure metals increases with rise in temperature. iv) Ohm’s law is a relation between the power used, the current and the potential difference in a circuit. v) A series circuit has only one conducting path for the electrons that move through it, a parallel circuit has multiple conducting paths. vi) A conducting wire offers resistance to the flow of electrons because electrons repel each other in the wire. 5) How many electrons are present in 1 coulomb charge? 6) Express the charge of an electron in coulombs. 7) Magnanin is used for making standard resistors. Why? 8) A copper wire of resistivity ρ is stretched to reduce its diameter to half of the previous value? What is its new resistivity? –6 –6 –6 9) Resistivities of copper, silver and constantan are 1.18 ×10 Ω cm, 1 ×10 Ω cm, 48 ×10 Ω cm. Which is the best resistor, why? 10) Name three devices, which make use of heating effect of current.

volt commonly known as? ampere 12) Name the scientist who gave the relation between PD and Current. coulomb ? 13) What is s e cond 11) What is

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14) a) The resistivities of a few substances at 20°C is given below. Which of them is the best heating element? –8 –6 ii) Manganin 44 × 10 Ωm i) Copper 1.62 × 10 Ωm iii) Nichrome 100 × 10 Ωm –6

iv) Silver 1.6 × 10

–8

Ωm

b) What do the following symbols stand for? 15) Draw a circuit diagram, showing a resistor, 3 cells, a plug key in series. Show the direction of current. 16) State ohm’s law. 17) Define electric power. Short Answers Questions: 2 Marks 18) What are the S.I. and commercial units of electrical energy? How are they related to each other? 19) Explain the following: a) Why is tungsten used almost exclusively for filament of incandescent lamps? b) Why are the conductors of electric heating devices, such as toasters and electric irons, made of an alloy rather than a pure metal? c) How does the resistance of a wire vary with its cross-sectional area? 20) Distinguish between kilowatt-hour and kilowatt. 21) a) State the law which relates current and potential difference. b) What happens to the constant of proportionality in the above law when the length of the wire is increased? 22) Two wires A and B are of the same metal, have same area of cross section and length in the ratio 4:1. What will be the ratio of current flowing through them when same potential difference is applied? 23) What happens to the resistance of a conductor if its length is doubled and radius is halved? 24) a) Draw the graph of current and potential difference for a metallic conductor b) Define 1 ohm Short Answers Questions: 3 Marks 25) State three factors on which the heat produced in a conductor depends. 26) Give the characteristics of a material used for making heating elements? 27) A piece of wire having resistance R, is cut into four equal parts. i) How will the resistance of each part compare with the original resistance? ii) If the four parts are placed in parallel, how will the resistance of the combination compare with the resistance of the original wire? 28) A piece of wire is redrawn by pulling it until its length is doubled. Compare the new resistance with original value. 29) Name the instrument used for measuring P.D. Draw a diagram showing how this instrument is connected in a circuit. 30) Name the instrument used for measuring current. Draw a diagram showing how this instrument is connected in a circuit. CW Exercise: (Problems) 1) Calculate the time taken by 60 W bulb to consume 3000 J of energy. 2) An electric bulb consumes 3600 Joules of energy in one minute. Calculate its power. 3) An electric motor uses 40J of energy in 5 seconds. What is its power? 4) In how much time will a 60W bulb consume 300 J of energy? Volume


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5) You are given three resistors of 10Ω, 15Ω, 20Ω, a battery of emf 3V, a key and an ammeter. Draw a circuit diagram placing 10Ω and 15Ω in series and the combination in parallel to 20Ω. 6) The electrical resistivity of some materials is given. Which of them is most suited for use in heating element? –8 A 5.20 × 10 Ωm –8 B 12.9 × 10 Ωm –6 C 100 × 10 Ωm 12 D 10 Ωm 7) You are given three resistors of 2Ω, 1Ω, 3Ω a battery of e.m.f. 1.5V, a key and an ammeter. Draw a circuit diagram showing the correct connections of all the components such that the ammeter reading is 1A. 8) Calculate the energy consumed by a 60-W bulb in half a minute if correct voltage is applied to it. 9) A 2V battery is connected across a small bulb. Calculate the resistance of the filament if 0.2A current flows. 10) Find the cost of electricity for running an electric motor of 1 HP for 5 hrs a day @ Rs.1.50 per unit for the month of November

A 11) Find total resistance across A and B

R

R

R

R

R

C 12)

60Ω

100Ω A

B

40Ω

Calculate the effective resistance across A and B.

B

B 1Ω A

13) Find the effective resistance between M and N 60Ω

A

60Ω

1Ω

C 1Ω

1Ω M

60Ω 60Ω

14)

1Ω

N

Calculate the Equivalent resistance across AB. B

15) 10 bulbs of resistance 50Ω each are connected in series to 200V mains. Find the current drawn. 16) Calculate the resistance between P and S.

1Ω P

4Ω

2Ω Q

3Ω

R

S

17) A copper wire has a diameter 0.5 mm and a resistivity of 1.6 ohm cm. How much of this wire would be required to make a 10 ohm coil? 18) Draw a schematic diagram of a circuit consisting of a battery of four 2 V cells, a 5 ohm resistor, an 8 ohm resistor, and a 12 ohm resistor, and a plug key, all connected in series. 19) Redraw the circuit above, putting in an ammeter to measure the current through the resistors and a voltmeter to measure the voltage across the 12 ohm resistor. What would be the readings in the ammeter and the voltmeter? 20) Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to a 220 V supply. What current is drawn from the supply line? 6Ω D 4Ω C E 21) In the circuit shown in fig. calculate 12Ω i) the current flowing through the arms AB, AC and CDE A B 1.5V ii) the potential difference across AB, CD and DE.

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22) A 40 watt lamp requires 0.182 A of current at 220 volts, while a 60 watt lamp requires 0.272 A of current at 200 volt line. If 40 W and 60 W lamp are connected in series to 220V, how many ampere of current will flow through each lamp? 23) Five dry cells each of 1.5 volt have internal resistance of 0.2, 0.3, 0.4, 0.5 and 12Ω when connected in series. What current will these five cells furnish through 10Ω resistance? 24) The values of current I, flowing in a given resistor for the corresponding values of potential difference V, across the resistor are given below: 0.5 1.0 2.0 3.0 4.0 I (ampere) V (volt) 25)

26) 27)

28) 29)

0.5

2.5

6.75

11.0

15.0

Plot a graph between V and I and calculate the resistance of the resistor. Calculate the resistance of 1 metre of copper wire that has a cross-sectional area of about –2 2 2 × 10 cm . Compare the value of this resistance with that of a flashlight bulb, which has a –8 power rating of 1W and operates at 3V. What does this comparison tell you? ρcu = 1.62×10 Ω m What is the resistance of an electric lamp if it uses 20A when connected to a 220 Volt line? Two wires A and B are of the same metal, have same area of cross section and lengths in the ratio of 2:1. What will be the ratio of current flowing through them respectively with same P.D. applied across each of them? A torch bulb is rated at 3 volt and 600 mA. Find its power and resistance. Three resistances 2Ω, 3Ω, 5Ω are connected in parallel. What is the equivalent resistance of the combination?

30) Find the equivalent resistance across PQ. 31) 3 resistances 5Ω, 10Ω, 30Ω respectively are connected in parallel to a 12V battery. Calculate (a) total resistance (b) current through each resistor. 32) Three resistance of 6Ω, 3Ω, 2Ω are connected in parallel. The combination of the above resistors is connected in series to a resistance of 4Ω and a cell of emf 1.5V. The internal resistance of the cell is negligible. a) Draw the circuit diagram. b) Calculate the current in main circuit. c) Find the current in each of the resistors in parallel. 33) Two wires A and B of the same metal are connected in series. Wire A has length l while wire B l has length , radius of wires being same for both. Find the ratio of the total resistance of series 2 combination and the resistance of A. 34) 100 J of heat is produced each second in a 4Ω resistance. Find the potential difference across the resistor. 35) Two bulbs are marked 60W, 220V and 60W, 110V respectively. Find the ratio of their currents.

HW Exercise: (Theory) Very Short Answer Questions: 1 Mark 1) Define electric current. 2) Define potential difference. 3) State Ohm’s Law. 4) What is the unit of electric charge? 5) Define 1 volt. 6) What is meant by 1 ampere of current? Volume


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7) 8) 9) 10) 11) 12) 13) 14) 15) 16) 17) 18) 19) 20)

What is the unit of resistance? Define 1 Ohm. What is Power? What is the SI unit of power? How many watts are equal to 1 horse–power? What is the heating element in electric bulb made of? What is a voltammeter? How many extra electrons are present on a body having 2 coulombs of negative charge? Which electrical quantity has the unit ohm–metre. What happens to the resistivity of a conductor if the length of the wire is reduced to half and radius of the wire is doubled? Define potential difference. Give its SI unit. Give the commercial unit of electrical energy. What is volt × ampere? The resistivities of a few substances at 20° C is given below. Arrange them in decreasing order 12 –6 –8 of their conductivity. (Glass = 10 Ω m, Nichrome = 100 × 10 Ω m, Silver = 1.6 × 10 Ω m, –8 Mercury = 94 × 10 Ω m).

Short Answer Questions: 2 Marks 21) Explain the concept of resistance. 22) Mention two applications of heating Effects of current. 23) State Joule’s law of heating effect. 24) Why is nichrome used in most heating devices? Short Answer Questions: 3 Marks 25) Derive an expression for three resistance connected in series. 26) Derive an expression for three resistance connected in parallel. 27) Explain the working of Electric bulb. 28) Draw a circuit diagram showing two resistances of 5Ω each in parallel and the combination in series with 10Ω. Connect the above combination to a cell, an ammeter and switch. Also show the direction of current. 29) Two lamps are rated 100W at 220V and the other 60W at 220V and are connected in parallel to a 220V supply. What is the current drawn from it. 30) State the characteristics of a fuse wire. 31) Why is household wiring done in parallel? HW Exercise: (Problems) 1) An electric iron consumes 1KW electric power when operated at 220V. What is the minimum rating of the fuse of be used for safe use of this device? 2) A 1000 W electric geyser is used everyday for one hour. How many units of electrical energy will it consume in 30 days? 3) A 200 watt bulb is lighted for two hours. How much energy is consumed? 4) A house is fitted with five 100 watt lamps. How many units of electrical energy are consumed by lighting the lamps for a month of 30 days at a rate of 2 hours a day? 5) An electric heater is used everyday for 120 minutes. The electricity bill for 30 days is 60 units. Calculate the power of the electric heater. 6) Calculate the energy supplied by 10 kilowatt of power in one hour. Give the answer in Joule. 150


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7) A 1000 W electric oven is used everyday for 90 minutes. Calculate the units of electrical energy this oven will consume in 30 days of use. 8) A shopkeeper used 1000W electric heater for 5 hours and 200 W electric bulb for 10 hours every day. Calculate the cost of using the heater and bulb for 20 days if the cost of one unit of electrical energy is one rupee. 9) A house contains 6 bulbs of 60W each, 3 fans of 80W each and a room heater of 500 W. If everything is operated for 4 hrs a day on the average, how many units of energy will be consumed in a month of 30 days? If electricity costs Rs.1.25 per unit, how much will be the cost of electricity used in the house in that month? 10) A parallel combination of three resistors takes a current of 7.5A from a 30V supply. If the two resistors are 10Ω and 12Ω, find the third one? 11) A lamp of 100 W works at 220volt. What is its resistance and current capacity? 12) A current of 5.0A flows through an electric press of resistance 11Ω. Calculate the energy consumed by the press in 5 minutes? 13) What will be the cost of running 500W heater for 20 hrs at the rate of Re. 0.80 per unit? 14) Two resistances connected in series have an effective value of 10Ω. When connected in parallel, the effective value is 2.5Ω. What are the values of the resistances? 15) Find the combined resistance between points A and B. 16) Three resistances 10Ω, 5Ω, 15Ω are connected in parallel. Find the equivalent resistance of the combination. 17) Raman performed an experiment by connecting a cell, an ammeter and different resistances as shown. What would the ammeter reading be in (b) and (c)?

18) Find the equivalent resistance across A and B. 2Ω

2Ω

A

2Ω

2Ω 2Ω

2Ω

2Ω

2Ω

2Ω B

19) A house contains 6 bulbs of 60W each, 3 fans of 80W each and a room heater 500 W. If each of them is used for four hours a day, find the cost of electrical energy for the month of September, if a unit costs Rs.1.85. 20) Find the equivalent resistance between A and B.

NCERT QUESTIONS: 1) What does an electric circuit mean? 2) Define the unit of current. 3) Calculate the number of electrons constituting one coulomb of charge. Volume


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4) 5) 6) 7) 8)

Name a device that helps to maintain a potential difference across a conductor. What is meant by saying that the potential difference between two points is 1 V? How much energy is given to each coulomb of charge passing through a 6 V battery? On what factors does the resistance of a conductor depend? Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why? 9) Let the resistance of an electrical component remain constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it? 10) Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal? 11) Use the data in table of resistivities at 20° C to answer the following: a) Which among iron and mercury is a better conductor? b) Which material is the best conductor? 12) Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 V each, a 5Ω resistor, an 8 Ω resistor, and a 12 Ω resistor, and a plug key, all connected in series. 13) Redraw the circuit of above Question, putting in an ammeter to measure the current through the resistors and a voltmeter to measure the potential difference across the 12Ω resistor. What would be the readings in the ammeter and the voltmeter? 6 14) Judge the equivalent resistance when the following are connected in parallel: (a) 1Ω and 10 Ω, 3 6 (b) 1 Ω and 10 Ω, and 10 Ω. 15) An electric lamp of 100 Ω, a toaster of resistance 50 Ω, and a water filter of resistance 500 Ω are connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances, and what is the current through it? 16) What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series? 17) How can three resistors of resistances 2 Ω, 3 Ω, and 6 Ω be connected to give a total resistance of (a) 4 Ω, (b) 1 Ω? 18) How can (a) the highest, and (b) the lowest total resistance be secured by the combinations of four coils of resistance 4 Ω, 8 Ω, 12 Ω, 24 Ω? 19) Why does the cord of an electric heater not glow while the heating element does? 20) Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V. 21) An electric iron of resistance 20 Ω takes a current of 5 A. Calculate the heat developed in 30 s. 22) What determines the rate at which energy is delivered by a current? 23) An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2 h. 24) How is a voltmeter connected in the circuit to measure the potential difference between two points? 25) A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10 Ω m. What will be the length of this wire to make its resistance 10Ω? How much does the resistance change if the diameter is doubled? 26) The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below: –8

I (amperes) 0.5 1.0 2.0 3.0 4.0 V (volts) 1.6 3.4 6.7 10.2 13.2 Plot a graph between V and I and calculate the resistance of that resistor.

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27) When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor. 28) A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4Ω, 0.5Ω and 12Ω, respectively. How much current would flow through the 12Ω resistor? 29) How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line? 30) Show how you would connect three resistors, each of resistance 6Ω, so that the combination has a resistance of (i) 9Ω, (ii) 4Ω. 31) Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A? 32) A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases? 33) Compare the power used in the 2 Ω resistor in each of the following circuits: i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and ii) a 4 V battery in parallel with 12 Ω and 2 Ω resistors. 34) Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V? 35) Which uses more energy, a 250 W TV set in 1 hr. or a 1200 W toaster in 10 minutes? 36) An electric heater of resistance 8 Ω draws 15 A from the service mains in 2 hours. Calculate the rate at which heat is developed in the heater. 37) Explain the following: a) Why is tungsten used almost exclusively for filament of electric lamps? b) Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal? c) Why is the series arrangement not used for domestic circuits? d) How does the resistance of a wire vary with its area of cross-section? e) Why are copper and aluminium wires usually employed for the transmission of electricity? PREVIOUS BOARD QUESTIONS: Very Short Answer Questions: (1 mark) 1) Draw a schematic diagram of an electric circuit consisting of a battery of two cells each of 1.5 V, 5Ω, 10Ω and 15Ω resistors and a plug key, all connected in series. [2009] 2) Why is a series arrangement not used for connecting domestic electrical appliances in a circuit? [AI 08] 3) Out of 60 W and 40 W lamps, which one has a higher electrical resistance when in use? [AI 08] 4) Why is much less heat generated in long electric cables than in filaments of electric bulbs? [Delhi 05] 5) Why is tungsten metal selected for making filaments of incandescent lamp bulbs? [Delhi 2005] 6) A wire resistance 10 ohm is bent in the form of a closed circle .What is the effective resistance between the two points at the ends of any diameter of the circle? [AI 05] 7) A wire resistance 20 ohm is bent in the form of a closed circle .What is the effective resistance between the two points at the ends of any diameter of the circle? [AI 05] 8) Should the heating element of an electric iron be made of iron, silver or nichrome wire? [Foreign 05]

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Short Answer Questions: (2 marks) 9) Calculate the resistance of an electric bulb which allows a 10 A current when connected to a 220 V power source. [2009] 10) What is an electric circuit? Distinguish between an open and a closed circuit. [2009] 11) A lamp rated 100 W at 220 V is connected to the mains electric supply. What current is drawn from the supply line if the voltage is 220 V? [2009] 12) An electric iron has a rating of 750 W, 220 V. Calculate i) current passing through it, and ii) its resistance, when in use. [Delhi 07] 13) An immersion heater has a rating of 2 kW, 220 V. While in use calculate i) current passing through it, and ii) its resistance. [Delhi 07] 14) An electric lamp is marked 100 W, 220 V. It is used for 5 hour daily. Calculate i) its resistance while glowing ii) energy consumed in kWh per day [AI 07] 15) An electric lamp is marked 40 W, 220 V. it is used for 4 hours daily. Calculate i) its resistance while glowing ii) energy consumed in kWh per day [AI 07] 16) An electric lamp is marked 25 W, 220 V. It is used for 10 hours daily. Calculate i) its resistance while glowing ii) energy consumed in kWh per day [AI 07] 17) An electric heater is used on 220 V supply and takes a current of 3.4 A. Calculate i) its power and ii) its resistance, when it is in use [Foreign 07] 18) One lamp is rated 40 W at 220 V and the other 60 W at 220 V. these two lamps are connected in parallel to a 220 V supply. Calculate the current drawn from the supply line by each lamp. [Foreign 07] 19) i) Draw a diagram to show how two resistors R1 and R2 are connected in series. ii) In a circuit if the two resistors of 5 ohm and 10 ohm are connected in series, how does the current passing through the two resistors compare? [AI 06] Short Answer Questions: (3 marks) 20) a) Define the term ‘volt’. b) State the relation between work, charge and potential difference for an electric circuit. Calculate the potential difference between the two terminals of a battery if 100 joules of work is required to transfer 20 coulombs of charge from one terminal of the battery to the other. [2009] 21) a) How is the direction of electric current related to the direction of flow of electrons in a wire? b) Calculate the current in a circuit if 500 C of charge passes through it in 10 minutes. [2009] 22) a) Define the term ‘coulomb’. b) State the relationship between the electric current, the charge moving through a conductor and the time of flow. Calculate the charge passing through an electric bulb in 20 minutes if the value of current is 200 mA. [2009] 23) a) Distinguish between the terms’ overloading’ and ‘short–circuiting’ as used in domestic circuits. b) Why are the coils of electric toasters made of an alloy rather than a pure metal? [AI 08] 24) Two lamps, one rated 40 W at 220 V and the other 100 W at 220 V, are connected in parallel to the electric supply at 220 V. a) Draw a circuit diagram to show the connections. b) Calculating the current drawn from the electric supply. c) Calculate the total energy consumed by the two lamps together when they operate for one hour [AI 08] 154


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25) An electric lamp of 200 Ω and a toaster of 100 Ω are connected in parallel to a 220 V electricity source. a) What will be the resistance of an electric iron which when connected to the same electric source permits the same current as the total current flowing through both the appliances described above? b) What is the current passing through the electric iron? c) Calculate the power of the electric iron? [Foreign 08] 26) Two lamps, one rated 60 W at 220 V and the other 40 W at 220 V, are connected in parallel to the electric supply at 220 V. a) Draw a circuit diagram to show the connections. b) Calculate the current drawn from the electric supply. c) Calculate the total energy consumed by the two lamps together when they operate for one hour. [AI 08] 27) a) State ohm’s Law. b) Draw a schematic diagram of the circuit for studying Ohm’s Law [AI 07] 28) a) What is meant by ‘Electric Resistance’ of a conductor? b) A wire of length L and resistance R is stretched so that its length is doubled and the area of cross–section is halved. How will its: i) resistance change? ii) resistivity change? [Delhi 07] 29) i) Draw a schematic diagram of a circuit consisting of a battery of five 2V cells, a 5 ohm resistor, a 10 ohm resistor and a 15 ohm resistor, and a plug key, all connected in series. ii) Calculate the electric current passing through the above circuit when the key is closed [Delhi 06] 30) i) Draw a schematic diagram of a circuit consisting of a battery of five 2V cells, a 5 ohm resistor, and a plug key, all connected in series. ii) Calculate the electric current passing through the above circuit when the key is closed. [Delhi 06] 31) Name the unit used in selling electrical energy to consumers. Two lamps, one rated 100 W at 220 V and the other 40 W at 220 V are connected in parallel to a 220 V mains supply. Calculate the electric current drawn from the supply line. [Foreign 06] 32) A torch bulb is rated 3.0 V and 600 mA. Calculate: i) its power, ii) its resistance and iii) the energy consumed if it is lighted for 4 hours. [Delhi 05] 33) Describe an activity to find the relationship between the potential difference across the two ends of a conductor and the current flowing through it by including in your answer the following: a) diagram of the electric circuit b) an observation table c) a V – I graph. [Foreign 08] Long Answer Questions: (5 mark) 34) a) What is the function of an earth wire in electrical instruments? Why is it necessary to earth the metallic electric appliances? b) Explain what is short circuiting and overloading in an electric supply. c) What is the usual capacity of the fuse wire in the line to feed, i) Lights and fans? ii) Appliances of 2 kW or more power? [Delhi 07] 35) a) State Ohm’s law. Write symbols used in electric circuits to represent i) variable resistance ii) voltmeter. b) Two resistors of resistances 4 Ω and 12 Ω are connected (i) in parallel, and (ii) in series. Calculate the values of effective resistance in each case. [Delhi 07]

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ANSWERS TO UNSOLVED EXERCISES: C.W Exercise: (Theory) 1) a) resistance b) Variable resistance c) Cell 2) a 4) i) False (ii) True (iii) True (iv) False (v) True (vi) False 18 18 –19 5) 6.25 × 10 electrons OR 6 × 10 6) –1.6 × 10 C 11) ohm 12) G.S. Ohm 13) Ampere 14) (a) iii C.W. Exercise: (Problems) 1) 50 s 2) 60 W 3) 8 W 4) 5 secs 6) C 7) R=1.5, 2Ω, 1Ω, in series 8) 1800 J 9) 10Ω 10) Rs.167.85 11) 5 R 12) 32Ω 13) 8/3Ω 14) 45Ω 15) 0.4A 16) 31/5 Ω –4 19) 0.32A, 3.84V 20) 0.727A 17) 1.227 × 10 m 21) 0.125A, 0.15A, 0.15A, 1.5V, 0.9V, 0.6V 22) 0.109 A 23) 0.319A –2 24) 4.12 Ω 25) 0.81 × 10 Ω, 9Ω, 0.0009 : 1 or 9:10,000 26) 11 Ω 27) 1:2 28) 1.8W, 5Ω 29) 30/31 30) 37.5Ω 31) R = 3Ω, 2.4A, 1.2A, 0.4A 32) 0.3A, 0.05A, 0.1A, 0.15A 33) 3:2 34) 20V 35) 1:4 H.W. Exercise (Theory): 4) coulomb 18 10) watt 14) 2 × 6.25 × 10 electrons 15) Resistivity 16) No change 18) Kilowatt hour 19) Watt 20) Silver, Mercury, Nichrome glass H.W. Exercise: (Problems) 1) 5 A and above 2) 30 units 3) 24000J 4) 30 units 7 5) 1 kW 6) 3.6 × 10 J 7) 45 kWh 8) Rs.140 9) 132 kW, Rs.165 10) 15Ω 11) 484 Ω, 0.455A 12) 82500J 13) Rs.8.00 14) 5Ω, 5Ω 15) 7Ω 16) 30/11 Ω 17) 0.05A, 0.2A 18) 18Ω 19) 132kWh,Rs.244.20 20) 22.5Ω NCERT: 1) A continuous and closed path of an electric current is called electric circuit 2) 5) 6) 8)

4) cell battery ampere 3) 6 × 10 electrons Means 1 J of work is done in moving a charge of 1 coulomb between 2 pts. 6J Thick wire as resistance (R) is inversely proportional to area of cross section 18

9) becomes half as V α I 5Ω 8Ω 12)

12Ω

A

6V

I=– 14) a)

156

6 = 0.24A 25

1 1 10 6 + 1 + 6 = 1 10 10 6

11) a) Iron (b) Silver 5Ω 13)

8Ω

12Ω V

6V

V = 0.24 × 12 = 2.88 V R=

10 6 = 0.999 Ω = (1 Ω app) 1000001


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10 6 1 1 1 1 10 6 + 10 3 + 1 =1+ + ⇒ = = = 9.9 Ω (10Ω approx.) 101001 R R 10 3 10 6 10 6

1 1 1 1 = + + RP 100 50 500

15)

⇒

1 5 + 10 + 1 16 500 ⇒ RP = Ω = 31.25 Ω = = 16 RP 500 500

v 220 Resistance of the electric iron is 31.25 Ω = × 16 = 7.04 A R 500 17) a) Yes. Connect 3Ω and 6Ω in parallel and the combination with 2Ω in series I=

1 1 1 1 = + = RP 3 6 2

∴ RP = 2

b) Yes, connect all three resisters in parallel,

R=2+2=4Ω

1 1 1 + + =1Ω 2 3 6

18) a) highest is in series, 4 + 8 + 12 + 24 = 48 Ω b)

1 1 1 1 1 1 6 + 3 + 2 + 1 12 24 ; ; RP = = 2Ω (lowest is in parallel) = + = + = = RP 4 8 12 24 RP 24 24 12

19) because resistance of the heating elements is much more than that of the cord. Hence, for the same current, heat produced in the heating element is more 2 20) H = I Rt = VI t = V × Q = 50 × 96000 = 4800000 J 2 22) Power 21) H = I RT = 25 × 20 × 30 = 15000 J 23) P = VI; 220 × 5 P = 1100 W = 1.1 KW E = P × t = 1.1 × 2 = 2.2 Kwh 24) Parallel 25) 122.7 m; ¼ times 27) 3.33 Ω 31) 4.8 kΩ 28) 0.67 A 29) 4 resistors 31) 110 bulbs 32) 9.2 A, 4.6 A, 18.3 A 33) (i) 12 W; (ii) 8 W 34) 0.73 A 35) 250 W TV set in 1 hour 36) 120 W

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Chapter 13: Magnetic Effects of Current Chapter Map: → Introduction ↓ Magnetism

↓ Properties

↓ Mapping

→ Magnetic effects of current ↓ Oerested’s Experiment

↓ Magnetic field due to straight wire

↓ Circular loop

→ Magnetic field due to Solenoid → Effects of external field on a wire carrying current ↓ Fleming’s Left Hand Rule

↓ Factors

↓ Electric Motor

→ Electromagnetic Induction ↓ Fleming’s Right Hand Rule

↓ Factors

↓ Generator

↓ DC / AC

→ Domestic Power Supply

Introduction: Magnetism:       

Magnets attract iron, nickel and cobalt. Every magnet has two poles – north and south poles. A freely and horizontally suspended bar magnet points N S north south direction. Like poles of 2 magnets repel each other and unlike poles attract. The space around a magnet is called magnetic field. Magnet field consists of magnetic field lines. Magnetic field is a quantity that has both direction and magnitude. The direction of the magnetic field at a point is given by the direction in which the north pole of a compass needle deflects at the point.

Properties of magnetic field lines: 

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They are directed from North Pole of the magnet to the South Pole externally and south to north, internally.


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

The relative strength of a magnet decreases as the distance from it increases. The magnetic field lines are closer where the field strength is more and are spaced where the strength is less.  Both the poles are of equal strength.  The field lines never intersect as they cannot have two directions at a given point.  The magnetic lines are curved outside the magnet and parallel within.

Magnetic lines of force around a bar magnet:

S

N

Magnetic Effects of Electric Current: Oersted’s Experiment:    

When a magnetic needle is placed near a wire carrying current, the needle shows deflection. This shows that the wire carrying current behaves as magnet. This effect of electric current is called magnetic effect of current. Magnetic effect of electric current was discovered by Hans Christian Oersted.

 The deflection of the magnetic needle depends on the direction of current and position of the wire.

Magnetic field due to a straight wire carrying electric current:  Since a wire carrying current produces magnetism there is a region around the wire where the effect can be felt.  This region is called magnetic field.  Magnetic field is represented by imaginary lines called as magnetic field lines.  These field lines are circular and may be in clockwise or anticlockwise direction depending on the direction of current in the wire.

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Factors affecting the magnetic field produced due to current:  The strength of magnetic field at a point:  is directly proportional to the strength of the current.  is inversely proportional to the distance of the point from the conductor.

The direction of magnetic field around a straight conductor: Right Hand Thumb rule: 

Imagine that you are holding a current-carrying straight conductor in your right hand with the thumb stretched and pointing in the direction of current. Then your fingers wrapped around the conductor give the direction of the magnetic field around the conductor. This is known as the right-hand thumb rule.

Magnetic field due to a current through circular loop:   

   

Suppose a straight wire is bent in the form of a circular loop and current is passed through it. The magnetic field produced at a point by a current-carrying wire varies inversely with its distance from the wire. At every point of a current-carrying circular loop, the concentric circles representing the magnetic field around it would become larger and larger as we move away from the wire. By the time we reach the centre of the circular loop, the arcs of these big circles would appear as straight lines. Every point on the wire carrying current would give rise to the magnetic field appearing as straight lines at the center of the loop. By applying the right hand thumb rule, it is easy to check that every section of the wire contributes to the magnetic field lines in the same direction within the loop. In a circular coil carrying current, if direction of current in the coil facing us is clockwise then that end has South Polarity. Similarly, if the direction of current in the coil facing us is anticlockwise, it is North Pole.

Magnetic field due to a Solenoid:  A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid.  It behaves as a magnet when current flows through it.  One end acts as North–pole and the other end acts as South–pole.  Its field is similar to that of a bar magnet.  Presence of a soft iron inside the coil increases its magnetism.  The field lines inside the solenoid are in the form of parallel straight lines spaced uniformly.  This indicates that the magnetic field is the same at all points inside the solenoid. That is, the field is uniform inside the solenoid.  A strong magnetic field produced inside a solenoid can be used to magnetise a piece of magnetic material, like soft iron, when placed inside the coil.  The magnet so formed is called an electromagnet.  Electromagnetism is temporary as it exists only during the presence of current in the coil. 160


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Difference between Electromagnets and Permanent Magnets: Electromagnets

Permanent Magnets

They are temporary magnets

The substance is permanently magnetized.

They lose magnetism when flow of current is stopped.

They lose magnetism on rough handling, hammering, heating etc.

Soft iron is electromagnets.

Steel, Chromium steel, Cobalt steel, Tungsten steel, Alnico and Nipermag are used for permanent magnets.

used

for

making

Note: Alnico is an alloy of Aluminium, Nickel, Cobalt, Nipermag is an alloy of Iron, Nickel, Aluminium and titanium.

Effects of External Field on a wire carrying current:



What is the effect of an external magnetic field on a conductor carrying current?

Ans: i) An electric current flowing through a conductor produces a magnetic field around the conductor. ii) The field so produced exerts a force on a magnet placed in the vicinity of the conductor. ii) The magnet must also exert an equal and opposite force on the current-carrying conductor. iv) Due to this force, the conductor deflects or rotates. v) When a conductor carrying current is placed in an external magnetic field, it experiences a force. This force is perpendicular to its length and the magnetic field. vi) The direction of this force is given by Fleming’s Left Hand Rule.

Fleming’s Left hand Rule:  Stretch the thumb, fore finger and middle finger of your left hand such that they are perpendicular to each other.  If the fore finger points in the direction of magnetic field and the middle finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor. Note: 1) Moving charges when placed in a magnetic field experience a force. This effect is used in the construction of particle accelerators. 2) Particle accelerators produce high energy particles which are used to study the structure of matter. 3) The high energy particles from the sun on entering the earth’s magnetic field experience a force and get trapped near the earth’s magnetic equator. This region is called Van Allen Radiation Belt.

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Factors to increase the force:  Increase the number of turns of the wire.  Increase the strength of the current.  Use Powerful Magnets.

Electric Motor:  An electric motor is a rotating device that converts electrical energy to mechanical energy.  Electric motor is used as an important component in electric fans, refrigerators, mixers, washing machines, computers, MP3 players etc. N S

Construction: 

An electric motor, consists of a rectangular coil ABCD of insulated copper wire.  The coil is placed between the two poles of a magnet such that the arm AB and CD are perpendicular to the direction of the magnetic field.  The ends of the coil are connected to the two halves P and Q of a split ring.  The inner sides of these halves are insulated and attached to an axle. The external conducting edges of P and Q touch two conducting stationary brushes X and Y, respectively.

Working:   

     



162

Current in the coil ABCD enters from the source (battery) through conducting brush X and flows back to the battery through brush Y. The current in arm AB of the coil flows from A to B. In arm CD it flows from C to D, that is, opposite to the direction of current through arm AB. On applying Fleming’s left hand rule for the direction of force on a current-carrying conductor in a magnetic field, it is seen that the force acting on arm AB pushes it downwards while the force acting on arm CD pushes it upwards. Thus the coil and the axle O, mounted free to turn about an axis, rotate anti-clockwise. At half rotation, Q makes contact with the brush X and P with brush Y. Therefore the current in the coil gets reversed and flows along the path DCBA. A device that reverses the direction of flow of current through a circuit is called a commutator. In electric motors, the split ring acts as a commutator. The reversal of current also reverses the direction of force acting on the two arms AB and CD. Thus the arm AB of the coil that was earlier pushed down is now pushed up and the arm CD previously pushed up is now pushed down. Therefore the coil and the axle rotate half a turn more in the same direction. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil and the axle. The commercial motors use  an electromagnet in place of permanent magnet;  large number of turns of the conducting wire in the current carrying coil; and  a soft iron core on which the coil is wound. Universal Tutorials – X CBSE (2012–13) – Physics

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The soft iron core, on which the coil is wound, plus the coils is called an armature. This enhances the power of the motor.

Electromagnetic Induction:  When a coil is connected to a galvanometer and a magnet is moved in and out of it, the galvanometer shows deflection.  Electricity is induced in the coil due to the motion of the magnet.  This phenomenon of production of electricity is called electromagnetic induction and the Current is called induced current.  It was observed that a relative motion of a magnet and a coil induces current or e.m.f. (electromotive force) in the coil.  It was discovered by Michael Faraday.  Methods to produce induced current  We can induce current in a coil either by moving it in a magnetic field or by changing the magnetic field around it.  It is convenient in most situations to move the coil in a magnetic field.

Fleming’s Right Hand Rule:  When the thumb, forefinger and central finger of the right hand are stretched perpendicular to each other, and if thumb gives direction of motion of the coil and fore finger gives direction of magnetic field then central finger gives the direction of induced current.

Magnetic field

Motion of the conductor

Induced current

Factors to increase the strength of induced current:  Increase the number of turns of the wire.  Increase the speed of rotation of the coil.  The direction of rotation of the coil is at right angles to the magnetic field.

Generator: 

In an electric generator, mechanical energy is used to rotate a conductor in a magnetic field to produce electricity.

N

S

Construction: 

An electric generator consists of a rotating rectangular coil ABCD placed between the two poles of a permanent magnet.  The two ends of this coil are connected to the two rings R1 and R2. Volume


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164     

The inner side of these rings are made insulated. The two conducting stationary brushes B1 and B2 are kept pressed separately on the rings R1 and R2, respectively. The two rings R1 and R2 are internally attached to an axle. The axle may be mechanically rotated from outside to rotate the coil inside the magnetic field. Outer ends of the two brushes are connected to the galvanometer to show the flow of current in the given external circuit.

Working:         



When the axle attached to the two rings is rotated such that the arm AB moves up (and the arm CD moves down) in the magnetic field produced by the permanent magnet. If the coil ABCD is rotated clockwise in the arrangement. By applying Fleming’s right-hand rule, the induced currents are set up in these arms along the directions AB and CD. Thus an induced current flows in the direction ABCD. If there are larger number of turns in the coil, the current generated in each turn adds up to give a large current through the coil. This means that the current in the external circuit flows from B2 to B1. After half a rotation, arm CD starts moving up and AB moving down. As a result, the directions of the induced currents in both the arms change, giving rise to the net induced current in the direction DCBA. The current in the external circuit now flows from B1 to B2. Thus after every half rotation the polarity of the current in the respective arms changes. Such a current, which changes direction after equal intervals of time, is called an alternating current (abbreviated as AC). This device is called an AC generator.

Direct Current:     

A steady current which flows only in one direction is called D.C. (direct current). To get a direct current (DC, which does not change its direction with time), split-ring commutators are used instead of slip ring. With this arrangement, one brush is at all times in contact with the arm moving up in the field, while the other is in contact with the arm moving down. Thus a unidirectional current is produced. The generator is thus called a DC generator.

Alternating Current:  1  A current which changes direction after equal intervals of time  s in india.  is called  100  Alternating Current (A.C.)  It can be transmitted to long distances without much loss of energy.  Its frequency is 50 Hz in India. 

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Domestic Electric Circuits:  In our homes, we receive supply of electric energy through a main supply (also called mains), either supported through overhead electric poles or by underground cables.  One of the wires in this supply, usually with red insulation cover, is called live wire (or positive, or phase).  Another wire, with black insulation, is called neutral wire (or negative).  In our country, the potential difference between the two is 220 V.  At the metre-board in the house, these wires pass into an electricity meter through a main fuse.  Through the main switch they are connected to the line wires in the house.  These wires supply electricity to separate circuits within the house.  Currently, two separate circuits are used, one of 15 A current rating for appliances with higher power ratings such as geysers, air coolers etc.  The other circuit is of 5 A current rating for bulbs, fans etc.  The earth wire, which has insulation of green colour, is usually connected to a metal plate deep in the earth near the house.  This is used as a safety measure, especially for those appliances that have a metallic body.  For example, electric press, toaster, table fan, refrigerator etc. the metallic body is connected to the earth wire, which provides a low-resistance conducting path for the current.  Thus, it ensures that any leakage of current to the metallic body of the appliance keeps its potential to that of the earth, and the user may not get a severe electric shock.  In each separate circuit, different appliances can be connected across the live and neutral wires. Each appliance has a separate switch to ‘ON’/‘OFF’ the flow of current through it. In order that each appliance has equal potential difference, they are connected parallel to each other.  A fuse in a circuit prevents damage to the appliances and the circuit due to overloading.  Overloading can occur when the live wire and the neutral wire come into direct contact.  This occurs when the insulation of wires is damaged or there is a fault in the appliance.  In such a situation, the current in the circuit abruptly increases (provides low resistance path).  This is called short-circuiting (live and neutral wire come in direct contact).  The use of an electric fuse protects the electric circuit and the appliance from a possible damage by stopping the flow of unduly high electric current.  The heating that takes place in the fuse melts it to break the electric circuit.  Overloading can also occur due to an accidental hike in the supply voltage.  Sometimes overloading is caused by connecting too many appliances to a single socket. APPENDIX: Activity 13.1: Take a straight thick copper wire and place it between the points X and Y in an electric circuit, as shown in Fig. 13.1. Place a small compass near to this copper wire. See the position of its needle. Pass the current through the circuit by inserting the key into the plug. Observe the change in the position of the compass needle. Volume


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Ans: The needle is deflected. It means that the electric current through the copper wire has produced a magnetic effect. Thus we can say that electricity and magnetism are linked to each other. Activity 13.2: Fix a sheet of white paper on a drawing board using some adhesive material. Place a bar magnet in the centre of it. Sprinkle some iron filings uniformly around the bar magnet (Fig.). A salt-sprinkler may be used for this purpose. Now tap the board gently. What do you observe? Ans: The iron filings arrange themselves in a pattern. The magnet exerts its influence in the region surrounding it. Therefore the iron filings experience a force. The force thus exerted makes iron filings to arrange in a pattern. Activity 13.3 (Experiment): Aim: Mapping the line of force around the bar magnet Apparatus: Paper, Bar magnet, magnetic compass Procedure: Step


1)

Take a small compass and a bar magnet.

––

2)

Place the magnet on a sheet of white paper fixed on a drawing board, using some adhesive material.

––

3)

Mark the boundary of the magnet.

––

4)

Place the compass near the north pole of the magnet. How does it behave?

The south pole of the needle points towards the north pole of the magnet. The north pole of the compass is directed away from the north pole of the magnet

5)

Mark the position of two ends of the needle.

––

6)

Now move the needle to a new position such that its south pole occupies the position previously occupied by its north pole.

––

7)

In this way, proceed step by step till you reach the south pole of the magnet.

––

8)

Join the points marked on the paper by a smooth curve.

This curve represents a field line.

9)

Repeat the above procedure and draw as many lines as you can.

10)

Observe the deflection in the compass needle as you move it along a field line.

These lines represent the magnetic field around the magnet. These are known as magnetic field lines.

The deflection increases as the needle is moved towards the poles. Conclusion: The magnetic lines of force emerge from N–pole & move towards south externally. Activity 13.4: Take a long straight copper wire, two or three cells of 1.5 V each, and a plug key. Connect all of them in series. Place the straight wire parallel to and over a compass needle. Plug the key in the circuit. 166


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Ans: If the current flows from north to south, the north pole of the compass needle would move towards the east. This would result in the change of the direction of current through the copper wire, that is, from south to north. The needle moves in opposite direction, that is, towards the west. It means that the direction of magnetic field produced by the electric current is also reversed. Activity 13.5: Take a battery (12 V), a variable resistance (or a rheostat), an ammeter (0–5 A), a plug key, and a long straight thick copper wire. Insert the thick wire through the centre, normal to the plane of a rectangular cardboard. Take care that the cardboard is fixed and does not slide up or down. Connect the copper wire vertically between the points X and Y, in series with the battery, a plug and key. Sprinkle some iron filings uniformly on the cardboard (You may use a salt sprinkler for this purpose). Keep the variable of the rheostat at a fixed position and note the current through the ammeter. Close the key so that a current flows through the wire. Ensure that the copper wire placed between the points X and Y remains vertically straight. Gently tap the cardboard a few times. Observe the pattern of the iron filings. Ans: The iron filings align themselves showing a pattern of concentric circles around the copper wire. They represent the magnetic field lines. The direction of the north pole of the compass needle would give the direction of the field lines produced by the electric current through the straight wire at point. Activity 13.6: Take a rectangular cardboard having two holes. Insert a circular coil having large number of turns through them, normal to the plane of the cardboard. Connect the ends of the coil in series with a battery, a key and a rheostat, as shown in Fig. Sprinkle iron filings uniformly on the cardboard. Plug the key. Tap the cardboard gently a few times. Note the pattern of the iron filings that emerges on the cardboard. Ans: The iron filings arrange themselves in a definite pattern around the wire as shown in the diagram.

Activity 13.7: Take a small aluminium rod AB (of about 5 cm). Using two connecting wires suspend it horizontally from a stand, as shown in Fig. Place a strong horse-shoe magnet in such a way that the rod lies between the two poles with the magnetic field directed upwards. For this put the North Pole of the magnet vertically below and South Pole vertically above the aluminium rod. Connect the aluminium rod in series with a battery, a key and a rheostat. Now pass a current through the aluminium rod from end B to end A. What do you observe? Reverse the direction of current flowing through the rod and observe the direction of its displacement. Why does the rod get displaced? Volume


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Ans: i) It is observed that the rod is displaced towards the left. ii) It is now towards the right. iii) The rod gets displaced because it experiences a force due to the two magnetic fields. Activity 13.8: Take a coil of wire AB having a large number of turns. Connect the ends of the coil to a galvanometer. Take a strong bar magnet and move its north pole towards the end B of the coil. Do you find any change in the galvanometer needle? Ans: There is a momentary deflection in the needle of the galvanometer. This indicates the presence of a current in the coil AB. The deflection becomes zero the moment the motion of the magnet stops. The galvanometer needle is deflected towards the left, showing that the current is now set up in the direction opposite to the first. The galvanometer needle deflects toward the right when the coil is moved towards the north pole of the magnet. Similarly the needle moves toward left when the coil is moved away. When the coil is kept stationary with respect to the magnet, the deflection of the galvanometer drops to zero. Conclusion: Motion of magnet produces current in the coil. Activity 13.9: Take two different coils of copper wire having large number of turns (say 50 and 100 turns respectively). Insert them over a non-conducting cylindrical roll. (You may use a thick paper roll for this purpose.) Connect the coil-1, having larger number of turns, in series with a battery and a plug key. Also connect the other coil-2 with a galvanometer as shown. Plug in the key. Observe the galvanometer. Is there a deflection in its needle? Ans: The needle of the galvanometer instantly jumps to one side and just as quickly returns to zero, indicating a momentary current in coil-2. It means that now the current flows in the opposite direction in coil-2. Conclusion: We can induce current in a coil either by moving it in a magnetic field or by changing the magnetic field around it. It is convenient in most situations to move the coil in a magnetic field. SOLVED EXAMPLES:

Magnetic field

1) A current through a horizontal power line flows in east to west direction. What is the direction of magnetic field at a point directly below it and at a point directly above it? Ans: The current is in the east-west direction. Applying the right-hand thumb rule, we get that the direction of magnetic field at a point below the wire is from north to south. The direction of magnetic field at a point directly above the wire is from south to north. 2) An electron enters a magnetic field at right angles to it, as shown in Fig. The direction of force acting on the electron will be a) to the right b) to the left c) out of the page d) into the page Electron Ans: d. The direction of force is perpendicular to the direction of magnetic field and current as given by Fleming’s left hand rule. Recall that the direction of current is taken opposite to the direction of motion of electrons. The force is therefore directed into the page.

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REVIEW QUESTION:

CW Exercise: (Theory) Very Short Answer Questions: 1 Mark 1) What is an electromagnet? 2) When can an electric charge give rise to magnetic field? 3) State the direction in which the needle will turn in the given diagram? 4) What is your observation if current is reversed in fig. 3 5) What is the polarity at B in fig., when the key is closed? 6) If a soft iron core is inserted in a solenoid, what happens to its magnetic property? 7) Check the following statements. Write true or false against each. a) Like magnetic poles attract each other, unlike poles repel. b) If you strike a sharp edge of a metallic knife against the North Pole of a bar magnet, it will induce a north pole. c) The magnetic field produced by a current in a straight wire has no poles 8) The phenomenon of electromagnetic induction is a) The process of charging a body. b) The process of generating magnetic field due to a current passing through a coil. c) Producing induced current in a coil by relative motion between a magnet and the coil. d) The process of rotating a coil of an electric motor. 9) What are magnetic field lines? How is the direction of a magnetic field at a point determined? Mention two important properties of the magnetic field lines. 10) Name the device used for measuring potential difference. 11) The figure shows the direction of current in a straight conductor. Show the direction of lines of force. Short Answer Questions: 2 Marks 12) How will the magnetic field set up by a solenoid change when (a) current is decreased (b) soft iron core is introduced into it. 13) Diagram shows a coil AB, connected to a center zero galvanometer G. The galvanometer shows deflection to the right, when the North pole of a powerful magnet is moved to right? Q.13 a) Why does deflection occur? b) Is current in the coil in anticlockwise or clockwise when viewed from end A? 14) Give two differences between electromagnets and permanent magnets? 15) Draw a diagram to show field lines of magnetic field through and around a solenoid carrying current. 16) Answer the following questions: A B i) Copy the diagram in your paper and show the direction of current. ii) Mark the polarity of A. iii) Why does end A and B behave as magnets? Q.16 iv) Who discovered this effect? Volume


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17) On what factors does the force experienced by a straight conductor carrying current placed in a uniform magnetic field depend? Short Answer Questions: 3 Marks 18) On what factors does the magnitude of induced e.m.f. depend? 19) State the factors on which the force experienced by a straight conductor placed in a magnetic field depends: 20) State: (i) Fleming’s right hand rule. (ii) Fleming’s Left Hand Rule (iii) Thumb Rule. Which of these laws are most suitable for finding the direction of magnetic field in a Straight conductor? 21) A fixed copper coil of many turns is connected to a galvanometer. A movable permanent magnet is shown. What are your observations? i) Magnet is moved rapidly in the direction of arrow. ii) The magnet is stopped within the coil. iii) Magnet is pulled rapidly out of the coil. Q.21 22) A coil of copper wire is connected to a galvanometer. What would happen if a bar magnet is: a) Pushed into the coil with its north pole entering first? b) Pulled out of the bar magnet? c) Held stationary inside the coil? 23) Explain what is short-circuiting and overloading in an electric supply. 24) Describe the action of an electric fuse. 25) What happens if fuse wire is placed in parallel in you household wiring? 26) Two fuse wires of same length are rated 15A and 5A. Which of the two will be thicker and why? 27) Answer the following: a) Who discovered the magnetic effects of current? b) Name the rule used to find the direction of magnetic field around a straight wire carrying current. c) Mention two important properties of magnetic field lines. 28) Two coils of insulated copper are wound on a bunch of nails as shown. Answer the following questions: a) What happens in the second coil when current is switched on in the st 1 Coil? Why? nd st b) What do you observe in the 2 Coil when the 1 Coil is disconnected? Why? Q.28 c) What is the above phenomena and who experimented it? 29) Take a small aluminium rod AB. Suspend it horizontally by means of two connecting wires from a stand as shown. Place a strong horseshoe magnet in such a way that the rod is between the poles with the field directed upwards. If current is now passed in the rod from B to A. a) What do you observe? Q.29 b) What is the cause of this observation? c) What would happen if you reverse the direction of current or interchange the poles of the magnet? 30) With respect to magnetic effects of current answer the following questions. a) What happens to the deflection of the magnetic needle placed at a point, if the current in the wire is increased? b) What happens to the deflection of the magnetic needle if the wire is moved away from the needle, current remaining same? 170


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c) What is the direction of deflection of the North pole of the magnetic needle in the given diagram Wire carrying current

S

N

d) State the rule which gives the direction of lines of force around a wire carrying current. 31) i) Identify the two objects shown ii) give any two differences between them. Soft iron S

N

a)

b)

32) A student performs an experiment to study the magnetic effect of current around a straight wire carrying current. He reports that i) the direction of deflection of the north pole of a compass needle kept at a given point near the conductor remains unaffected even when the terminals of the battery sending current in the wire are inter changed. ii) for a given battery, the degree of deflection of the N-pole decreases when the compass is kept at a point farther away from the conductor. Which of the above observations of the student is incorrect and why? 33) A current time graph is shown in A and B i) Identify the type of current in each case ii) Name a device each which produces such a current. + max A) B) I Ι O

O

t – max

→ time

HW Exercise: (Theory) Very Short Answer Questions: 1 Mark 1) Name the scientist who discovered the magnetic effect of current. 2) Give the direction of deflection of the North Pole of the magnetic needle when a wire carrying current from south to north is placed below the magnetic needle. 3) A wire is carrying current in upward direction. What is the direction of lines of force? 4) State the rule, which helps us to determine the direction of lines of force. 5) Which polarity is acquired by the circular coil on the side facing you? 6) What is a solenoid? 7) What happens when a magnet is moved towards a coil of wire? Q.5 8) State Fleming’s Left Hand Rule. 9) What information does Fleming’s Right Rand Rule give? 10) Define Electromagnetic Induction. 11) Name the scientist who discovered electromagnetic induction. 12) Name the law, which gives the direction of induced e.m.f. Volume


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13) Name the rule used to find the force experienced by a conductor carrying current placed in a magnetic field. 14) What is meant by short – circuit? 15) The figure shows a loop of wire carrying current. Show the lines of force around it. Q.15 Short Answer: 2 Marks 16) On what factors does the deflection of magnetic needle depend when placed in the vicinity of a wire carrying current? 17) Draw the diagram of a solenoid and show the polarity? 18) Explain the effect of external magnetic field on a wire carrying current? 19) Explain Electromagnetic induction. 20) Give difference between ac and dc. 21) Draw a rough sketch of the pattern of field lines due to a: a) current flowing into a circular coil and b) solenoid carrying current 22) State the laws: a) To find the direction of lines of force around a straight wire carrying current. b) To find the direction of motion of the coil carrying current placed in a magnetic field. Short Answer: 3 Marks 23) Describe Oersted’s experiment to show that a current carrying conductor produces a magnetic field? 24) What is a solenoid? Draw a diagram representing magnetic field around a solenoid when direct current flows through it. How will you find its polarity without using a magnetic needle? 25) Explain the working of Fuse wire. 26) A fixed copper coil of many turns is connected to a galvanometer. A movable permanent magnet is shown. What is your observations when the magnet is moved along the direction of the arrow? a) What is the phenomenon known as? Define it. A B S b) Who discovered the above phenomenon? G c) Name a device that works based on the above phenomenon. Q.26 Long Answer: 5 Marks 27) Explain the Domestic circuit. 28) The diagram shows a solenoid in which a soft iron core is inserted. Copy the diagram and on it mark: B A a) Direction of flow of current. b) Direction of flow of electrons c) Magnetic polarity at ends A and B d) Suggest a way of increasing the strength of the magnet. e) What type of a magnet is a solenoid permanent or temporary? 29) State the rule to determine the direction of, Q.28 a) magnetic field produced around a current carrying conductor. b) force experienced by a straight conductor carrying current placed in a magnetic field, which is perpendicular to it. c) current induced in a circuit by the changing magnetic flux due to the motion of a magnet. 30) On what factors does the force experienced by a current carrying conductor placed in a uniform magnetic field depend? 172


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NCERT QUSESTIONS: 1) 2) 3) 4) 5)

6) 7)

8)

9)

10)

11) 12) 13) 14) 15) 16) 17) 18)

19) 20) 21) 22)

23)

24)

Why does a compass needle get deflected when brought near a bar magnet? Draw magnetic field lines around a bar magnet. List the properties of magnetic lines of force. Why don’t two magnetic lines of force intersect each other? Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop. The magnetic field in a given region is uniform. Draw a diagram to represent it. Choose the correct option. The magnetic field inside a long straight solenoid-carrying current a) is zero b) decreases as we move towards its end c) increases as we move towards its end d) is the same at all points Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer) a) mass b) speed c) velocity d) momentum In Activity 13.7, how do we think the displacement of rod AB will be affected if i) current in rod AB is increased; ii) a stronger horse-shoe magnet is used; and iii) length of the rod AB is increased? A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is a) towards south b) towards east c) downward d) upward State Fleming’s left-hand rule. What is the principle of an electric motor? What is the role of the split ring in an electric motor? Explain different ways to induce current in a coil. State the principle of an electric generator. Name some sources of direct current. Which sources produce alternating current? Choose the correct option. A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each a) two revolutions b) one revolution c) half revolution d) one-fourth revolution Name two safety measures commonly used in electric circuits and appliances. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220V) that has a current rating of 5 A. What result do you expect? Explain. What precaution should be taken to avoid the overloading of domestic electric circuits? Which of the following correctly describes the magnetic field near a long straight wire? a) The field consists of straight lines perpendicular to the wire. b) The field consists of straight lines parallel to the wire. c) The field consists of radial lines originating from the wire. d) The field consists of concentric circles centred on the wire. The phenomenon of electromagnetic induction is a) the process of charging a body. b) the process of generating magnetic field due to a current passing through a coil. c) producing induced current in a coil due to relative motion between a magnet and the coil. d) the process of rotating a coil of an electric motor. The device used for producing electric current is called a a) generator b) galvanometer c) ammeter d) motor

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25) The essential difference between an AC generator and a DC generator is that a) AC generator has an electromagnet while a DC generator has permanent magnet. b) DC generator will generate a higher voltage. c) AC generator will generate a higher voltage. d) AC generator has slip rings while the DC generator has a commutator. 26) At the time of short circuit, the current in the circuit a) reduces substantially b) does not change c) increases heavily d) vary continuously 27) State whether the following statements are true or false. a) An electric motor converts mechanical energy into electrical energy. b) An electric generator works on the principle of electromagnetic induction. c) The field at the centre of a long circular coil carrying current will be parallel straight lines. d) A wire with a green insulation is usually the live wire of an electric supply. 28) List three sources of magnetic fields. 29) How does a solenoid behave like a magnet? Can you determine the north and south poles of a current–carrying solenoid with the help of a bar magnet? Explain. 30) When is the force experienced by a current–carrying conductor placed in a magnetic field largest? 31) Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field? 32) Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor? 33) Name some devices in which electric motors are used. 34) A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil? 35) Two circular coils A and B are placed close to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason. 36) State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field. 37) Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes? 38) When does an electric short circuit occur? 39) What is the function of an earth wire? Why is it necessary to earth metallic appliances? PREVIOUS BOARD QUESTIONS: Very Short Answer Questions: (1 mark) 1) How is the induced current in a secondary coil related to current in a primary coil? [2009] 2) State the rule which gives the direction of magnetic field associated with a current–carrying conductor. [2009] 3) Define the term ‘induced current’. [2009] 4) When is the force experienced by a current–carrying conductor placed in a magnetic field the largest? [2009] 5) How is an electromagnet different from a permanent magnet? [Foreign 08] 6) How is the magnitude of magnetic field produced by a current carrying straight conductor affected by increasing the strength of electric current flowing through it. [AI 07C] 174


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7) 8) 9) 10)

Why is the series arrangement not used for domestic electric circuits? [AI 07 C] Why is it necessary to earth the electrical appliances with metallic bodies? [AI 07 C] What constitutes the field of a magnet? [Delhi 06] What is the advantage of the third wire of earth connection in domestic electric appliances? [Delhi 06] 11) How can you show that the magnetic field produced by a given electric current in the wire decreases as the distance from the wire increases? [AI 06] 12) How will you use a solenoid to magnetic a steel bar? [Foreign 06] 13) How can we use a magnetic field to generate electricity? [Foreign 06] 14) How can it be shown that a magnetic field exists around a wire through which a direct electric current is passing? [Delhi 04] Short Answer Questions: (2 marks) 15) Calculate the electric consumed by a 1200 W toaster in 20 minutes. [2009] 16) What is meant by the term, ‘magnetic field’? Why does a compass needle show deflection when brought near a bar magnet? [AI 08] 17) Draw a diagram to show the magnetic field lines around a bar magnet. List any two properties of magnetic field lines [AI 08] 18) Describe an activity to show that a magnetic field is produced by an electric current flowing through a circular coil of wire. [Foreign 08] 19) A coil of copper wire is connected to a galvanometer as shown in the figure. What would happen to the deflection in the galvanometer if a bar magnet is i) pushed into the coil with its north pole entering first. ii) pulled out of the coil? [AI 07 C] Short Answer Questions: (3 mark) 20) What is the function of an electric fuse? Name the material used for making a fuse. In a household circuit where is fuse connected? Distinguish between overloading and short– circuiting. [Delhi 07 C] 21) What are magnetic field lines? Draw a diagram of field lines due to a bar magnet. Mark arrows on these lines to represent their directions [Delhi 07 C] 22) a) State Fleming’s left hand rule. b) Describe an activity to show that a current carrying straight conductor experiences a force when kept perpendicular to a magnetic field. [Delhi 07 C] Long Answer Question: (5 marks) 23) a) What is an electromagnet? b) List any of its two uses. c) Draw a labelled diagram to show how an electromagnet is made. d) What is the purpose of the soft iron core used in making an electro magnet? [AI 07] 24) a) Describe with diagram an experiment to show that a force is exerted on a current carrying conductor when placed perpendicular in a magnetic field. b) State the rule to find the direction of the force exerted on a current carrying conductor in a magnetic field. [Foreign 07] 25) i) What is an electromagnet? What does it consist of? [AI 06] ii) Name one material in each case which is used to make a a) permanent magnet b) temporary magnet iii) Describe an activity to show how you can make an electromagnet in your school laboratory. 26) a) What are ‘magnetic field lines’? How is the direction of a magnetic field at a point determined? b) Draw two field lines around a bar magnet along its length on its two sides and mark the field directions on them by arrow marks. c) List any three properties of magnetic field lines [Delhi 05] Volume


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27) Why is pure iron not used for making permanent magnets? Name one material used for making permanent magnets. Describe how permanent magnets are made electrically. State two examples of electrical instruments made by using permanent magnets [Delhi 05] 28) State ‘Fleming’s right hand rule’. With a labelled diagram, describe the working of an AC electric generator. [AI 05] 29) a) Draw a schematic labelled diagram of a domestic electric circuit which includes i) a main fuse ii) a power meter iii) a light point iv) a fan and v) a power plug b) Why is it necessary to connect an earth wire to the metallic electric appliances having metallic covers? [Delhi, Foreign 05] ANSWERS TO UNSOLVED EXERCISES: CW Exercise: (Theory) 7) a) False (b) False (c) False (d) False

8) c

H.W. Exercise: (Theory) 1) Oersted 3) Anticlockwise 5) North

2) East 4) Right Hand Thumb Rule 11) Faraday

10) Voltmeter

NCERT: 1) because a compass needle is a small magnet 4) Then they would have two different directions which is not possible. ↑↑↑ 7) d 8) c, d 9) increases in all cases c 15) Electromagnetic Induction 16) Cell, battery Oscillating, generator 18) c 22) d c 24) a 25) d 26) c (a) False (b) True (c) True (d) False 31) vertically downwards i) The needle will move momentarily in one direction ii) The needle will move momentarily but in opposite direction to (i) iii) No deflection in the needle would be observed. 36) (a) Right-hand thumb rule, (b) Fleming’s left-hand rule, (c) Fleming’s right hand rule.

6) 10) 17) 23) 27) 34)

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Chapter 14: Sources of Energy

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Chapter 14: Sources of Energy Chapter Map: → Introduction → A good source of energy → Fossil fuels → Disadvantages → Pollution control → Various uses of fossil fuels → Thermal Power Plant → Hydro Power Plant → Improvement in technology using Conventional sources ↓ Bio–mass

↓ Wind Energy

→ Biogas

→ Advantage

→ Advantages

→ Limitations

→ Non conventional sources ↓ Solar Energy

↓ Energy from sea

↓ Geothermal Energy

→ Solar Cooker

→ Tidal

→ Water heater

→ Wave

→ Solar cells

→ Ocean thermal

↓ Nuclear Energy

→ Environmental Sources → How long will an energy source last us?

Introduction:  According to the law of conservation of energy, ‘Energy is neither created nor destroyed’. It only gets converted into different forms.  Why then is the energy crisis? It is because the energy in the usable form is dissipated to the surroundings in less usable forms. Hence, any source of energy we use to do work is consumed and is not available for further use.

Fuel: 

Volume

A substance which produces good amount of heat on burning in air at a moderate temperature is a fuel. Universal Tutorials – X CBSE (2012–13) – Physics

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A good source of energy:  A good source of energy  should do a large amount of work per unit volume or mass.  should burn easily.  should have high calorific value  should not produce smoke and other pollutants  should not leave any residue  should be economical  should be easily available and  should be easy to transport and store.  The amount of heat energy released on burning a unit mass of a fuel completely is called its calorific value.

Conventional Sources of Energy: Renewable: 

The sources which provide us with a steady supply of energy or the sources which can be regenerated are termed as renewable sources of energy eg. solar energy, wind energy.

Non-Renewable: 

Sources of energy that would get depleted and cannot be replenished are non–renewable sources eg. fossil fuels like coal, petrol etc.  Those sources, which have accumulated in nature over a long time and cannot be quickly replaced when exhausted, are called non-renewable sources of energy.  Example: Coal, Natural gas, Petroleum, Lignite, and Uranium.  Classifying sources of energy as renewable & non-renewable has the following advantages:  It helps us to decide which of them has to be conserved.  The knowledge of non–renewable sources has compelled us to look for alternative sources. Hence new technologies have been developed.

Fossil Fuels:  Wood was the most common source of heat energy.  The energy of flowing water and wind was also used for limited activities.  Increasing industrialisation has led to a better quality of life all over the world. It has also caused the global demand for energy to grow at a tremendous rate.  The growing demand for energy was largely met by the fossil fuels – coal and petroleum.  These fuels were formed over millions of years ago and there are only limited reserves. The fossil fuels are non-renewable sources of energy, so we need to conserve them.

Disadvantages:  Burning fossil fuels has many disadvantages.  The oxides of carbon, nitrogen and sulphur that are released on burning fossil fuels are acidic oxides.  These lead to acid rain which affects our water and soil resources.

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 In addition to the problem of air pollution, the green-house effect of gases like carbon dioxide is also caused.

Pollution Control:  The pollution caused by burning fossil fuels can be somewhat reduced by increasing the efficiency of the combustion process and using various techniques to reduce the escape of harmful gases and ashes into the surroundings. Note: Besides being used directly for various purposes like gas stoves and vehicles, fossil fuels are the major fuels used for generating electricity.

Traditional sources of energy: Thermal Power Plant:  Large amount of fossil fuels are burnt every day in power stations to heat up water to produce steam which runs the turbine to generate electricity.  The transmission of electricity is more efficient than transporting coal or petroleum over the same distance.  Therefore, many thermal power plants are set up near coal or oil fields.  The term thermal power plant is used since fuel is burnt to produce heat energy (thermal energy) which is converted into electrical energy.

Hydro Power Plants:  Another traditional source of energy is the kinetic energy of flowing water or the potential energy of water stored at a height.  Hydro power plants convert the potential energy of falling water into electricity.  Since there are very few water-falls which could be used as a source of potential energy, hydro power plants are associated with dams.  A quarter of our energy requirement in India is met by hydro power plants.  In order to produce hydel electricity, high-rise dams are constructed on the river to obstruct the flow of water and thereby collect water in larger reservoirs.  The water level rises and in this process the kinetic energy of flowing water gets transformed into potential energy.  The water from the high level in the dam is carried through pipes, to the turbine, at the bottom of the dam transforming P.E. to K.E.  Since the water in the reservoir would be refilled each time it rains (hydro power is a renewable source of energy)

Constructions of big dams have certain problems associated with it: 

The dams can be constructed only in a limited number of places, preferably in hilly terrains.  Large areas of agricultural land and human habitation are to be sacrificed as they get submerged.  Large eco-systems are destroyed when submerged under the water in dams.

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The vegetation which is submerged rots under anaerobic conditions and gives rise to large amounts of methane which is also a green-house gas.  It creates the problem of satisfactory rehabilitation of displaced people. Note: Opposition to the construction of Tehri Dam on the river Ganga and Sardar Sarovar project on the river Narmada are due to such problems.

Improvements in Technology for using Conventional Sources of Energy: Bio-Mass:  Wood has been used as a fuel for a long time.  If we can ensure that enough trees are planted, a continuous supply of fire-wood can be assured.  Another example is cow-dung cakes as a fuel.  Since these fuels are plant and animal products, the source of these fuels is said to be biomass.  These fuels, however, do not produce much heat on burning and a lot of smoke is given out when they are burnt. They also leave a lot of residue on burning.  Therefore, technological inputs to improve the efficiency of these fuels are necessary.  When wood is burnt in a limited supply of oxygen, water and volatile materials present in it get removed and charcoal is left behind as the residue.  Charcoal burns without flames, is comparatively smokeless and has higher heat generation efficiency/ higher calorific value.

Bio gas and bio gas plant: 

      



Cow-dung, various plant materials like the residue after harvesting the crops, vegetable waste and sewage are decomposed in the absence of oxygen to give bio-gas. Since the starting material is mainly cow-dung, it is popularly known as ‘gobar-gas’. Bio-gas is produced in a plant. The plant has a dome-like structure built with bricks. A slurry of cow-dung and water is made in the mixing tank from where it is fed into the digester. The digester is a sealed chamber in which there is no oxygen. Anaerobic micro-organisms that do not require oxygen decompose or break down complex compounds of the cow-dung slurry. It takes a few days for the decomposition process to complete and generate gases like methane, carbon dioxide, hydrogen and hydrogen sulphide. Methane is the major component of bio–gas. The bio-gas is stored in the gas tank above the digester from which they are drawn through pipes for use.

Advantages of Bio gas: 

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It burns without smoke, leaves no residue (like wood, charcoal and coal on burning). Its heating capacity is high. Bio-gas is also used for lighting. The slurry left behind is removed periodically and used as an excellent manure, rich in nitrogen and phosphorous. The large-scale utilization of bio-waste and sewage material provides a safe and efficient method of waste-disposal besides supplying energy and manure.

Wind Energy:  The unequal heating of the landmass and water bodies by solar radiation generates air movement and causes winds to blow.  This kinetic energy of the wind can be used to do work.  This energy was harnessed by windmills in the past to do mechanical work – lifting of water for irrigation, pounding of grains etc.  Wind energy is used to generate electricity.  A windmill essentially consists of a structure similar to a large electric fan that is erected at some height on a rigid support.  To generate electricity, the rotatory motion of the windmill is used to turn the turbine of the electric generator.  The output of a single windmill is quite small and cannot be used for commercial purposes.  Therefore, a number of windmills are erected over a large area, which is known as wind energy farm.  The energy output of each windmill in a farm is coupled together to get electricity on a commercial scale.

Advantages: 

Wind energy is an environment-friendly and efficient source of renewable energy.  It requires no recurring expenses for the production of electricity.

Limitation:      

Firstly, wind energy farms can be established only at those places where wind blows for the greater part of a year. The wind speed should also be 15 km/h or more to maintain the required speed of the turbine. There should be some back-up facilities (like storage cells) to take care of the energy needs during a period when there is no wind. Establishment of wind energy farms requires large area of land. For a 1 MW generator, the farm needs about 2 hectares of land. The initial cost of establishment of the farm is quite high. Moreover, since the tower and blades are exposed to the vagaries of nature like rain, Sun, storm and cyclone, they need a high level of maintenance.

Non–conventional Sources:  As our demand for energy increases, we need to look for more and more sources of energy. We could develop the technology to use the available or known sources of energy more efficiently and also look to new sources of energy.

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 Any new source of energy we seek to exploit would need specific devices developed with that source in mind.

Solar Energy:  The Sun has been radiating an enormous amount of energy at the present rate for nearly 5 billion years and will continue radiating at that rate for about 5 billion years more.  Only a small part of solar energy reaches the outer layer of the earth’s atmosphere. Nearly half of it is absorbed while passing through the atmosphere and the rest reaches the earth’s surface.

Principle of Solar Heating Devices:  

Black body absorbs maximum heat. Green house effect.

Solar Cooker: 





Sun

Su (Su n -ray n sh s i ne )

Glass sheet G cover Container with food to be cooked (painted black from

Reflector (Plane mirror) R Inner metal box (painted black from inside)

A solar cooker is a device that is used to B cook food by solar energy. Being a slow Outer wooden box (having thermocol heater, the nutrients in the food cooked in lining inside) a solar cooker are not destroyed. Two types of solar cookers are available depending on the type of the reflector used. 1) Box – type 2) Spherical Reflector Type Temperature attained – 100° to 140°C

Construction Features: Inner Metal Box:  The Solar cooker consists of a metal box, which is painted all black from inside. Outer Wooden Box:  This houses the solar cooker and acts as an insulator. Food Container:  The food container is painted black from outside to maximize heat absorption. Reflector:  Reflector receives the sunlight and sends it (reflects) to the top of the Solar Cooker in the form of strong beams of sunlight. A spherical or parabolic reflector concentrates the light falling on them to the focus, thus increasing the temperature. Glass Sheet Cover:  This allows passing through the shorter infrared rays from the sun, but prevents any heat loss due to radiation of longer infrared rays from the cooker.

Solar Water Heater: 

A device in which water is heated by using solar energy  These water heaters are very commonly used in Northern India, where availability of Sunlight is ample

Construction: Storage Tank:  Cold water enters the storage tank, from where it circulates through the connecting pipes into the copper tubes. Insulated Box:  This houses the copper tubes, which receive the solar energy. The box is painted black to maximize heat absorption. 182


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Glass Lid:  The insulated box containing the copper tubes is sealed in a glass casing to produce the Green House effect. Copper tubes:  Copper being a very good conductor of heat, is used to maximize heat transfer inside the insulated box. It is here where the sunrays heat water.  The tube is coiled to increase the surface area for heating. Pipes – Insulated:  Insulated pipes are used as connecting pipes to avoid heat loss to the surroundings

Main cold water line Solar Radiation Hot water to tap

a) A solar water heater.

b) Schematic arrangement of a solar water heater.

Working:  

As water slowly moves through the pipe, it absorbs heat. Hot water being lighter remains in the upper part of the tank and the heavier cold water at the bottom.

Solar Cells: 

Solar cells convert solar energy into electricity.  A typical cell develops a voltage of 0.5–1 V and can produce about 0.7 W of electricity when exposed to the Sun.  A large number of solar cells are combined in an arrangement called solar cell panel that can deliver enough electricity for practical use. Advantage: 



The principal advantages associated with solar cells are that they have no moving parts, require little maintenance and work quite satisfactorily without the use of any focusing device. Another advantage is that they can be set up in remote and inaccessible hamlets or very sparsely inhabited areas in which laying of a power transmission line may be expensive and not commercially viable.

Disadvantage:    

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Silicon, which is used for making solar cells, is abundant in nature but availability of the special grade silicon for making solar cells is limited. The entire process of manufacture is still very expensive. Silver used for interconnection of the cells in the panel further adds to the cost. In spite of the high cost and low efficiency, solar cells are used for many scientific and technological applications. Universal Tutorials – X CBSE (2012–13) – Physics

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Uses: 



 

Artificial satellites and space probes like Mars orbiters use solar cells as the main source of energy. Radio or wireless transmission systems or TV relay stations in remote locations use solar cell panels. Traffic signals, calculators and many toys are fitted with solar cells. The solar cell panels are mounted on specially designed inclined roof tops so that more solar energy is incident over it.

Energy from Sea: Forms of energy from Sea: Tidal Energy: 

Due to the gravitational pull of mainly the moon on the spinning earth, the level of water in the sea rises and falls.  This phenomenon is called high and low tides and the difference in sea-levels gives us tidal energy.  Tidal energy is harnessed by constructing a dam across a narrow opening to the sea.  A turbine fixed at the opening of the dam converts tidal energy to electricity. Limitation: 

The locations where such dams can be built are limited.

Wave Energy: 

The kinetic energy possessed by huge waves near the seashore can be trapped in a similar manner to generate electricity.  The waves are generated by strong winds blowing across the sea.  Wave energy would be a viable proposition only where waves are very strong.  A wide variety of devices have been developed to trap wave energy for rotation of turbine and production of electricity.

Ocean Thermal Energy:      

The water at the surface of the sea or ocean is heated by the Sun while the water in deeper sections is relatively cold. This difference in temperature is used to obtain energy in ocean-thermal-energy conversion plants. These plants can operate if the temperature difference between the water at the surface and water at depths up to 2 km is 293 K (20°C) or more. The warm surface-water is used to boil a volatile liquid like ammonia. The vapours of the liquid are then used to run the turbine of generator. The cold water from the depth of the ocean is pumped up and condenses vapour again to liquid.

Note: The energy potential from the sea (tidal energy, wave energy and ocean thermal energy) is quite large, but efficient commercial exploitation is difficult.

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Geothermal Energy:  Due to geological changes, molten rocks formed in the deeper hot regions of earth’s crust are pushed upward and trapped in certain regions called ‘hot spots’.  When underground water comes in contact with the hot spot, steam is generated.  Sometimes hot water from that region finds outlets at the surface. Such outlets are known as hot springs.  The steam trapped in rocks is routed through a pipe to a turbine and used to generate electricity.

Limitation: 

The cost of production would not be much, but there are very few commercially viable sites where such energy can be exploited.

Note: There are number of power plants based on geothermal energy operational in New Zealand and United States of America.

Nuclear Energy:  Nuclear energy is generated by a process called nuclear fission  The nucleus of a heavy atom (such as uranium, plutonium or thorium), when bombarded with lowenergy neutrons, can be split apart into lighter nuclei.  When this is done, a tremendous amount of energy is released if the mass of the original nucleus is just a little more than the sum of the masses of the individual products.  The fission of an atom of uranium, for example, produces 10 million times the energy produced by the combustion of an atom of carbon from coal.  In a nuclear reactor designed for electric power generation, such nuclear ‘fuel’ can be part of a self–sustaining fission chain reaction that releases energy at a controlled rate.  The released energy can be used to produce steam and further generate electricity.

Disadvantages:     

The major hazard of nuclear power generation is the storage and disposal of spent or used fuels. The uranium continuously decays into harmful subatomic particles (radiations). Improper nuclear-waste storage and disposal result in environmental contamination. There is a risk of accidental leakage of nuclear radiation. The high cost of installation of a nuclear power plant, high risk of environmental contamination and limited availability of uranium makes large-scale use of nuclear energy prohibitive.

Note: Nuclear energy was first used for destructive purposes before nuclear power stations were designed.

Environmental Consequences:  Exploiting any source of energy disturbs the environment in some way or the other.  In any given situation, the source we would choose depends on factors such as the ease of extracting energy from that source, the economics of extracting energy from the source, the efficiency of the technology available and the environmental damage that will be caused by using that source. Volume


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 For example ‘clean’ fuels like CNG, means a particular source is cleaner than the other.  Burning fossil fuels causes air pollution.  In some cases, the actual operation of a device like the solar cell may be pollution-free, but the assembly of the device would have caused some environmental damage.  Research continues in these areas to produce longer lasting devices that will cause less damage throughout their life.

How long will an energy source last us?  We cannot depend on the fossil fuels for much longer as such sources will get depleted some day.  These sources are non-renewable sources of energy.  On the other hand, if we manage bio-mass by replacing the trees we cut down for fire-wood, we can be assured of a constant supply of energy at a particular rate.  Such energy sources that can be regenerated are called renewable sources of energy.  Renewable energy is available in our natural environment, in the form of some continuing or repetitive currents of energy or is stored in such large underground reservoirs that the rate of depletion of the reservoir because of extraction of usable energy is practically negligible. REVIEW QUESTION: CW Exercise 1: (Theory) Very Short Answer Questions: 1 Mark 1) Give suitable examples of the use of solar energy in daily life. 2) Name any two renewable sources of energy. 3) Mention any two uses of wind energy. 4) Name the device which directly converts solar energy into electrical energy. 5) Mention two ways by which water can be used to produce hydro-electricity. 6) State the limitations of wind energy. 7) Why is tidal energy not likely to be a potential source of energy? Short Answer Questions: 2 Marks 8) A windmill is being used to operate a pump for lifting water from a tube well to a tank at some height above the ground. List any four steps in sequence in which the energy gets transformed from one form to another in this process. 9) Mention any four areas where solar cells are being used as a source of energy. 10) State the forms in which energy stored in the oceans manifests itself. Which one of these is utilized in OTEC Systems? 11) State the advantages of obtaining biogas from animal dung and bio wastes. 12) A student constructed a model of a box–type solar cooker. He used transparent plastic sheet to cover the open face of the box. He found that his cooker did not function well. What modification should be made to enhance its efficiency? Give reason. 13) If you wished to set up a wind farm, what would be your main consideration in selecting the site? Short Answer Questions: 3 Marks 14) Why is hydro energy considered an indirect source of solar energy? Explain how hydro energy can be converted into electrical energy. State two advantages of hydro energy 15) Describe the construction of a solar cooker. How does it cause a rise in temperature to cook food? 186


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16) A student constructed a box-type solar cooker. He found that it did not work efficiently. What could this be due to? Give any four possible mistakes in the construction and operation of the solar cooker. What maximum temperature can ordinarily be reached inside a solar cooker? 17) Name the agent which decomposes animal dung into biogas. Describe the method of obtaining biogas. Name the main constituent of biogas. 18) Draw a labeled diagram of any one design of a biogas plant and describe its working. Mention any two advantages of converting animal dung into biogas over using it as fuel in the form of dried cakes. 19) What are the main constituents of biogas? Describe with a labeled diagram how it is prepared in a biogas plant. 20) Why biogas is considered superior to dry animal dung as a fuel? Draw a neat-labeled diagram of biogas plant? 21) Explain tidal energy. Long Answer Questions: 5 Marks 22) A student has set up a solar cooker in a box by using a black painted aluminium sheet, a black cooking vessel, some glass wool, a glass sheet and a mirror plate. i) What is the role of each item used in the solar cooker? ii) Draw a possible diagram for the set up. HW Exercise: (Theory) Very Short Answer Questions: 1 Mark 1) What is a solar cell? State its uses? 2) What is wind energy? 3) Name the process which, when successful, will convert oceans into an everlasting source of energy. 4) Give two examples of non-conventional sources of energy. 5) What is the difference between solar cell and a solar panel? 6) Flowing water can rotate a turbine. Which type of the energy does the turbine use up? 7) What is meant by hydroelectric power? 8) What is the need for an alternate source of energy? 9) What is biomass? Explain how biomass is used as a fuel. 10) Name a liquid whose vapours can be used in OTEC power plants. 11) Why are the copper pipes in a solar water heater coiled? Short Answer Questions: 2 Marks 12) What do you understand by the term ‘solar panel’? What are its uses? 13) Which property of water in oceans enables it to act as a storehouse of solar energy? 14) Name the three forms of energy, which could be harnessed from the oceans. 15) Why is it not possible to make use of solar cells to meet all our energy needs? State at least two reasons to support your answer. 16) What is meant by Ocean Thermal Energy? 17) With the help of a diagram explain the working of a biogas plant. Give three advantages of using biogas. 18) a) What is biogas? b) Name the agent responsible for converting biomass into biogas. Short Answer Questions: 3 Marks 19) Draw a diagram to show the basic design of a box type solar cooker 20) Write a short note on the design of solar heating device and also state some of its drawbacks. 21) Why is the copper tube of a solar water heater painted black from outside? Volume


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Long Answer: 5 Marks 22) With the help of a diagram, explain the construction and working of a box type solar cooker. 23) Explain the construction of solar water heater. 24) Explain the production of biogas by Biogas Plant. NCERT QUESTIONS: 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14) 15) 16) 17)

18) 19) 20) 21)

22) 23) 24)

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What is a good source of energy? What is a good fuel? If you could use any source of energy for heating your food, which one would you use and why? What are the disadvantages of fossil fuels? Why are we looking at alternate sources of energy? How has the traditional use of wind and water energy been modified for our convenience? What kind of mirror – concave, convex or plain – would be best suited for use in a solar cooker? Why? What are the limitations of the energy that can be obtained from the oceans? What is geothermal energy? What are the advantages of nuclear energy? Can any source of energy be pollution-free? Why or why not? Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not? Name two energy sources that you would consider to be renewable. Give reasons for your choices. Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices. A solar water heater cannot be used to get hot water on a) a sunny day b) a cloudy day c) a hot day d) a windy day Which of the following is not an example of a bio-mass energy source? a) wood b) gobar-gas c) nuclear energy d) coal Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy? a) geothermal energy b) wind energy c) nuclear energy d) bio-mass Compare and contrast fossil fuels and the Sun as direct sources of energy. Compare and contrast bio-mass and hydro electricity as sources of energy. What are the limitations of extracting energy from: a) the wind? b) waves? c) tides? On what basis would you classify energy sources as a) renewable and non-renewable? b) exhaustible and inexhaustible? Are the options given in (a) and (b) the same? What are the qualities of an ideal source of energy? What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility? What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?


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PREVIOUS YEARS’ BOARD QUESTIONS Very Short Answer Questions: (1 mark) 1) Which one of the following is a renewable resource? [AI 08] 2) Firewood is our conventional fuel. List any four replacing it by the alternate source of energy [AI 08] 3) Name an element used for making solar cells. [Delhi 07 C] 4) Write one application of solar cells. [Delhi 07 C] 5) State the energy transformation that takes place in a solar cell. [Delhi 07 C] 6) Name the process of large energy production in the Sun. [Delhi 06] Short Answer Questions: (2 marks) 7) What are fossil fuels? Give two examples of fossil fuels. [Foreign 08] 8) What is a solar cell panel? Write two advantages associated with such panels [Foreign 08] 9) Why is tidal energy not likely to be a potential source of energy? Give two reasons. [Delhi 07 C] 10) Write two applications of windmills, where are they mostly located in our country? [Delhi 07 C] 11) What is hydroelectricity? Why is solar energy considered an indirect source of hydroelectricity? [Delhi 07 C] 12) List four areas where solar cells are being used as a source of energy. [AI 07 C] 13) Draw a labelled diagram of fixed dome type biogas plant. [AI 07 C] 14) Name the type of nuclear reaction by which the Sun produces its energy. List two conditions which are present at the centre of the Sun responsible for this reaction. [AI 06] 15) Describe a nuclear chain reaction with an example. [Foreign 05] 16) Discuss one limitation each for the extracting of energy from: a) winds b) tides Short Answer Questions: (3 marks) 17) a) Why is the Solar Cooker box covered with a plane glass plate? [Delhi 07] b) Why is energy of water flowing in a river considered to be an indirect form of solar energy? 235 c) How is the fission of U92 nucleus?

18) a) State one limitation of solar energy available from solar cells. [AI 07] b) What is the minimum wind velocity required to obtain useful energy with a windmill? c) Define the term ‘nuclear fission’. 19) a) What is a ‘solar cell’? [Foreign 07] b) Why is bio–gas considered as an ideal fuel for domestic use? c) Name a device in which controlled chain reaction is used. 20) Explain the principle of working of a windmill. [Foreign 07] 21) a) What is a solar cell? b) Name any two areas where solar cells are being used as a source of energy. c) How is a nuclear chain reaction produced? [Foreign 07] 22) Define the terms nuclear fusion and nuclear fission. Give one example of each. [Delhi 07 C] 23) Define nuclear fusion and nuclear fission reactions. Why are nuclear fusion reactions not possible in school laboratories? [AI 07 C] Long Answer Questions: (5 marks) 24) i) Distinguish between renewable and non–renewable sources of energy giving one example of each. [Delhi 06] Volume


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ii) Why is the use of wood as a fuel not advised although forests can be replenished? 25) Explain why: [Delhi 06] i) It is difficult to burn a piece of wood fresh from a tree. ii) Pouring dry sand over the fire extinguished it. iii) It is difficult to use hydrogen as a source of energy. iv) Charcoal is considered a better fuel than wood. APPENDIX: Activity 14.1: List four forms of energy that you use from morning, when you wake up, till you reach the school. From where do we get these different forms of energy? Can we call these ‘sources’ of energy? Why or why not? Ans: Electrical, Heat, Chemical, Muscular and Light energy are the forms which we used from morning till we reach school. We get these forms from electricity, petrol and food. No, they are forms of energy. Activity 14.2: Consider the various options we have when we choose a fuel for cooking our food. What are the criteria you would consider when trying to categorise something as a good fuel? Would your choice be different if you lived? a) in a forest? b) in a remote mountain village or small island? c) in New Delhi? d) lived five centuries ago? How are the factors different in each case? Ans: i) Calorific value of the fuel ii) Whether the fuel would give out smoke/ leave a residue. iii) Easy availability of the fuel in required quantity. (a) Yes (b) availability of more heat (c) on gas (d) availability of the fuel It depends on the availability of the fuel, the amount of heat liberated and the extent of pollution caused Activity 14.3: Take a table-tennis ball and make three slits into it. Put semicircular ( ) fins cut out of a metal sheet into these slits. Pivot the tennis ball on an axle through its centre with a straight metal wire fixed to a rigid support. Ensure that the tennis ball rotates freely about the axle. Now connect a cycle dynamo to this. Connect a bulb in series. Direct a jet of water or steam produced in a pressure cooker at the fins (Fig. 14.2). What do you observe? Ans: The tennis ball with metal sheets act as turbine and generates electricity. This is the model to demonstrate thermo electric production. Therefore, the bulb glows. Activity 14.4: Find out from your grand-parents or other elders: a) how did they go to school? b) how did they get water for their daily needs when they were young? c) what means of entertainment did they use? 190


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Compare the above answers with how you do these tasks now. Is there a difference? If yes, in which case more energy from external sources is consumed? Ans: a) They went walking b) From wells they got water for their daily needs c) The means of entertainment they used were films in open air theatres We go by bus. The water we need is got from taps which are connected to the overhead tanks. Our mode of entertainment is films, T.V. and books. Energy in used more in present days. Activity 14.5: Take two conical flasks and paint one white and the other black. Fill both with water. Place the conical flasks in direct sunlight for half an hour to one hour. Touch the conical flasks. Which one is hotter? You could also measure the temperature of the water in the two conical flasks with a thermometer. Can you think of ways in which this finding could be used in your daily life? Ans: The black flask becomes hotter. We can use these finding in solar water heater and solar cookers. Activity 14.6: Study the structure and working of a solar cooker and/or a solar water-heater, particularly with regard to how it is insulated and maximum heat absorption is ensured. Design and build a solar cooker or water-heater using low-cost material available and check what temperatures are achieved in your system. Discuss what would be the advantages and limitations of using the solar cooker or water-heater. Ans: A black surface absorbs more heat as compared to white surface. Solar cookers and solar water heaters use this property. Some solar cooker achieves higher temperature by using mirrors for focusing the light. Solar cooker are covered with glass plate because glass allows short wavelength of infra red radiation in but does not allow long wavelength to escape. Activity 14.7: Discuss in class the question of what is the ultimate source of energy for bio-mass, wind and ocean thermal energy. Is geothermal energy and nuclear energy different in this respect? Why? Where would you place hydro electricity and wave energy? Ans: Biomass, wind and ocean energy are obtained from the sun. Geothermal and nuclear energy are not obtained from the sun. Hydro electricity and wave energy are obtained from the sun. Activity 14.8: Gather information about various energy sources and how each one affects the environment. Debate the merits and demerits of each source and select the best source of energy on this basis. Ans: Refer notes Activity 14.9: Debate the following two issues in class. a) The estimated coal reserves are said to be enough to last us for another two hundred years. Do you think we need to worry about coal getting depleted in this case? Why or why not? Volume


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b) It is estimated that the Sun will last for another five billion years. Do we have to worry about solar energy getting exhausted? Why or why not? On the basis of the debate, decide which energy sources can be considered (i) exhaustible (ii) inexhaustible, (iii) renewable and (iv) non-renewable. Give your reasons for each choice. Ans: We need to worry about the reserves of coal getting depleted because coal is a non–renewable source of energy. They take long time for their formation. Even though the sun will last for 5 billion years we need not worry about it getting exhausted because it is a very long time and human life span is very small. ANSWERS TO THE UNSOLVED EXERCISE: CW Exercise 1: (Theory) 1) Solar cooker and solar heater 2) Solar energy and wind energy 6) Solar cell / Photo cell NCERT: 15) b

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16) c

17) a, c


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Practical Skills in Science and Technology Electricity and Magnetism: 1) Two bulbs have power 100 W and 60 W respectively. Which bulb has greater resistance? a) 100 W b) 60 W c) Both have same d) Depends on the bulb 2) Resistance of a material does not depend on a) Length of the material b) Area of cross section of the material c) Time of passage of current. d) Nature of the material 3) The device used to measure current is a) Generator b) Voltmeter c) Motor d) Ammeter 4) The resultant resistance in the diagram is

10 3 5Ω 10Ω Ω b) Ω 3 10 c) 15 Ω d) 18 Ω The magnetic field inside a long straight solenoid carrying current a) is zero b) is less than that at the ends c) more than that at the ends d) same at all points Two bulbs have power 100 W and 60 W respectively. Through which bulb does more current flow for the same P.D a) 100 W b) 60 W c) Both are equal d) Depends on the bulb 1 kWh = _____ joules 6 5 7 a) 3.6 × 10 b) 36 × 10 c) 0.36 × 10 d) All the above At the time of short circuit, the current in the circuit a) Decreases b) Does not change c) Increases d) Varies continuously Find the effective resistance in the given diagram a)

5)

6)

7) 8) 9)

2 7Ω Ω 3Ω 7 4Ω 20 Ω c) 14 Ω d) 7 10) The magnetic field lines inside a solenoid carrying current a) are curved lines spaced far away b) are curved lines spaced closely c) are straight parallel lines d) are not present 11) Which of them does not represent Electrical Power? a)

7 Ω 2

a) V × I

b)

2

b) I R

c)

I2 R

Work done = Ch arg e a) Current b) Resistance c) Volt 13) The effective resistance in the given diagram is 59 7 Ω b) Ω a) 7 59 5Ω 109 c) Ω d) None of these 5

d)

V2 R

12)

Volume

d) Power 6Ω 12Ω 24Ω


193

194

14) The magnetic field around a straight conductor carrying current can be found using a) SNOW Rule b) Fleming’s Right hand Rule c) Fleming’s Left hand Rule d) Maxwell’s Right hand Rule 15) In an experiment to study dependence of current Ι on the potential difference across a given resistor, students kept the plug key in the circuit closed for time t1 and then open for time t2. The times t1 and t2 for students P, Q, R and S are given in the table below. Closed time t1 Open time t2 Student seconds seconds P 30 60 Q 60 30 R 60 15 S 45 15 The best choice of open and closed times is that of student: a) P b) Q c) R d) S 16) Which of the following does not have plus (+) or minus (–) signs marked on it? a) a resistor b) a voltmeter c) an ammeter d) a battery 17) Which is the correct arrangement for resistors connected in series? Rh r1

a)

Rh r2

Rh

b)

r1

r1

c)

r2

Ammeter

r2

d) None of these

Volmeter Ammeter

Volmeter

Volmeter

Ammeter

18) A student has to connect 4 cells of 1.5 V each, to from a battery of voltage 6V. Which of the connection is correct? a)

b)

c)

d)

19) The plot correctly showing the dependence of the current Ι on the potential difference V across a resister R is: I

I

A)

B)

o

C)

o o

a) A

v

I

I

o

b) B

v

D)

o

v

o o

o

c) C

v

d) D

20) Resistivity is also known as a) resistance b) specific resistance c) reciprocal of resistance d) reciprocal of resistivity 21) A current carrying conductor is a) positively charged b) negatively charged c) either positively or negatively charged d) neither positively nor negatively charged 22) Two resistors used singly or in series or in parallel give a resistance of 3Ω, 16Ω, 12Ω and 4Ω. The resistance of the resistors is a) 2 Ω and 6 Ω b) 7 Ω and 9 Ω c) 4 Ω and 12 Ω d) 3 Ω and 16 Ω 194


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23) A battery of emf E is connected in series with a resistance R and a voltmeter. An ammeter is connected in parallel with the battery then a) Only ammeter is likely to be damaged b) Only volt meter is likely to be damaged c) Both ammeter and voltmeter are likely to be damaged d) Neither ammeter nor voltmeter is likely to be damaged 6Ω 24) In the given circuit, the P.D across 3 Ω is 2Ω

2A

a) 2 V

3Ω

b) 4 V

4Ω

c) 8 V d) 16 V 25) The device always connected in parallel in an electric circuit is: a) voltmeter b) ammeter c) both voltmeter and ammeter d) rheostat 26) Key is plugged in the circuit only when readings have to be measured. This is done to stop: a) extra temperature b) burning of circuit c) extra energy loss d) all the above 27) For the circuits shown in fig. I and II, the ammeter readings would be: V

V

I)

II)

5

A

5

A 5V

5V

a) 1A in circuit I and 0A in circuit II b) 0A in both circuits c) 1A in both circuits d) 0A in circuit I and 1A in circuit II 28) The following apparatus is available in a laboratory: Battery : Adjustable from 0 to 4.5 volt Resistors : 3Ω and 6 Ω Ammeters : A1 of Range 0 to 3A; Least count 0.1 A : A2 of Range 0 to 1A; Least count 0.05 A Voltmeter : V1 of Range 0 to 10 V; Least count 0.5 V : V2 of Range 0 to 5 V; Least count 0.1 V The best combination of voltmeter and ammeter for finding the equivalent resistance of the resistors in series would be: a) ammeter A1 and voltmeter V1 b) ammeter A1 and voltmeter V2 c) ammeter A2 and Voltmeter V1 d) ammeter A2 and voltmeter V2 29) The normal positions of the pointers of the two ammeters A1 and A2 and two voltmeters V1 and V2 available in the laboratory were as shown. For an experiment to study the dependence of the current on the potential difference across a resistor, the student should select:

A1)

mA

A2)

a) ammeter A1 and voltmeter V1 c) ammeter A1 and voltmeter V2 Volume

mA

V1)

V2)

b) ammeter A2 and voltmeter V1 d) ammeter A2 and voltmeter V2


195

196

30) Positive terminal of an ammeter is connected with: a) negative terminal of the battery b) positive terminal of the battery c) negative terminal if the voltmeter d) none of these 31) If four 2Ω resistors are connected in parallel then the effective resistance of the combination is: a) 2Ω b) 8Ω c) 0.5Ω d) 4Ω 32) In an experiment to find the equivalent resistance of the series combination of the two resistors R1 and R2, a student uses the circuit shown here. The circuit will give: V a) correct reading for voltage V, but incorrect reading for current Ι b) correct reading for current Ι, but incorrect reading for voltage V c) correct reading for both current Ι and voltage V d) incorrect reading for both current Ι and voltage V

A R1 6V

R2

Battery eliminator

Range = 1A LC = 0.05A

33) The voltmeter, ammeter and resistance in the circuit shown have been checked to be correct. On plugging the key, the ammeter reads 0.9 A, but the voltmeter reads zero. This could be because: Range = 10V V LC = 0.5V a) the range of the voltmeter is more than the twice the battery voltage 5 b) the least count of the voltmeter is too high A 4.5V c) the wires joined to the voltmeter terminals are loose d) the voltmeter is incorrectly placed in the circuit 34) Which is the correct arrangement for resistors connected in parallel?

a)

b)

r1

r1

r2 Ammeter

r2

Volmeter

Ammeter Volmeter

c)

d) none of these

r1 r2 Volmeter Ammeter

35) Ohm’s law is true for: a) conductors b) insulators c) all materials 36) Equivalent resistance of the resistors in series is equal to: a) R = r1 + r2 + r3….. c)

b) R =

1 1 1 1 = + + + ... R r1 r2 r3

d)

d) semi–conductors

1 1 1 + + + ... r1 r2 r3

1 = r1 + r2 + r3 … R

37) A rheostat in an electric circuit is connected to: a) apply a variable resistance in the circuit b) apply a constant resistance in the circuit c) to start the flow of current in the circuit d) to stop the flow of current in the circuit 38) Coulomb is the SI unit of: a) current b) charge c) resistance d) potential difference 196


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39) The following apparatus is available in the laboratory: Battery Eleminator : Adjustable from 0 to 6 V Resistors : 3 Ω and 6Ω Ammeters : A1 of Range 0 to 5 A; Least count0.25 A : A2 of Range 0 to 3 A; Least count0.1 A Voltmeters : V1 of Range 0 to 10 V; Least count 0.5 V : V2 of Range 0 to 5 V; Least count 0.1 V For the experiment to find the equivalent resistance of the parallel combination of the two given resistors, the best choice would be: a) ammeter A1 and voltmeter V1 b) ammeter A1 and voltmeter V2 c) ammeter A2 and voltmeter V1 d) ammeter A2 and voltmeter V2 40) Which one of the following possesses more resistance? a) galvanometer b) ammeter c) voltmeter d) all of them posses equal resistance 41) Mathematically Ohm’s law is: Ι R 1 Ι a) V = ΙR b) V = c) V = d) = R Ι V R 42) Equivalent resistance of the resistors in parallel is equal to: 1 1 1 1 1 1 1 a) R = r1 + r2 + r3….. b) R = + + + ... c) = + + + ... d) none of these r1 r2 r3 R r1 r2 r3 43) During the verification of ohms law, the voltmeter and ammeter should be connected in such a way that a) Ammeter needle should deflect to the right and voltmeter needle to the left b) Ammeter needle should deflect to the left and voltmeter needle to the right. c) Both should deflect on the same side. d) none of the alone. 44) From the given readings, the resistance is a) 100 Ω b) 200 Ω c) 10 Ω d) 0.01 Ω 45) Resistances R1, R2 and R3 are connected as shown in circuits A and B. They are connected in

R2

A)

R2

B)

R1 A

V R3

R3 V

R1

()

() A a) Parallel in both b) Series in both c) Parallel in ‘A’ and series in ‘B’ d) Series in ‘A’ and parallel in ‘B’ 46) In the given circuit, the value of current in R2 is R1 = R 2.25 A a) 2.25 A b) 1.5 A 30Ω R =R c) 0.75 A 1.5 A E d) given information is insufficient 2

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197

198

47) In which of the circuits the equivalent resistance will be 4.8 Ω? 8Ω

I) I

I

12Ω I

II)

8Ω

12Ω

III) I

12Ω 8Ω

I

8Ω 12Ω

IV) I

I

I

I

a) I b) IV c) III d) II 48) A student has to connect 3 cells of 1.5V each to form a battery of 4.5 V. The correct way of connecting these cells is shown in figure A) B) C) D) None of them a) A b) B c) C d) D 49) Consider the given circuit. If a resistance R2 = R is connected parallel with R1 then a) The current through R1 will be halved R1 = R b) The P.D. across R1 remains V A c) The P.D. across R1, becomes less than V I d) current through R1 will be doubled ( ) V

V

6Ω 6Ω 6Ω

50) The voltmeter reading in the given circuit is a) zero b) 2 V c) 3 V d) 6 V A

( ) 6V

51) A 100 W bulb has resistance R1 and a 60W bulb has resistance R2. The relation between R1 and R2 is a) R1 > R2 b) R2 > R1 c) R1 = R2 d) none of them 52) Five bulbs are joined in parallel to a 3V battery as shown. A Each ammeter A1 to A5 reads 0.5 A. The ammeter A reads A1 a) 0:5 A b) 2.5 A A2 c) 1.2 A d) none of them A3 A4 A5

53) Which of the given statement about emf of a cell is wrong: a) emf is a force b) emf is greater than P.D. c) emf is equal to P.D. if no current is drawn from it d) All the above 54) In an experiment, a graph was plotted between P.D. (V) and current (I) by varying load rheostat. The conductance of the wire in the given graph is x x y a) b) v y x c) x × y

d) None of the above Ι

198


y Volume

Practical Skills

199

55) Two resistances r1 and r2(r1 < r2) are joined in parallel. The equivalent resistance R is such that a) R< r1 b) r1< R < r2 c) r2 < R < r1 + r2 d) R > r1 + r2 56) Two bulbs of wattages 25 and 100 respectively each rated 220V are connected in series with a supply of 440V. Which of the bulb / bulbs will fuse? a) 100 W b) 25 W c) both of them d) none of them 57) Three resistances of equal value are arranged in different combinations as shown. The increasing order of their equivalent resistance is 2Ω 2Ω I)

2Ω

2Ω

2Ω

II)

2Ω

2Ω

III)

2Ω

2Ω

2Ω

IV)

2Ω

2Ω

a) III < II < IV < I b) I < II < III < IV c) II < III < IV < I d) IV < III < II < I 58) A voltmeter is connected ___________ a) in series with the cell b) in parallel with the resistor c) in series with the resistor d) Any where in the circuit 59) Which of the following statements is correct? a) Resistance of a conductor is large whose slope of I–V is large. b) Resistance of a conductor is small whose slope of I–V is small c) Resistance of a conductor is large whose slope of I–V is small d) none of them 60) Unit of conductance is

ohm m 61) Two resistances r1 and r2 are joined in series (r1 < r2). Which of the following equations is correct if equivalent resistance is R. a) R = (r1 + r2) b) R > r1 + r2 c) R < r2 d) all of them 62) Correct set–up for ohm’s law verification is a) mho

b) ohm

c) ohmm

d)

A

A

a)

b) V

V

A

V

c)

Volume

A

d)

V


199

200

63) Three resistances of equal value are arranged as shown below. Arrange them in increasing order of power dissipated. R I)

Ι

R

R

R

II)

Ι

R R

R

III)

R

R

Ι

IV)

Ι

R

R R

a) I < II < III < IV b) IV < III < II < I c) II < III < I < IV d) III < II < IV < I 64) Which of the given statement about emf of a cell is correct? a) emf is a force b) emf may be less then P.D c) A cell does not set up an emf if no current flows d) emf is equal to P.D. if no current flows 65) A heater coil is cut into two equal parts and only 1 part is used in the heater. The heat generated as compared to the original value will be (PD remaining same)

1 1 b) c) 2 times 2 4 66) What is the ratio of heat generated in R and 2 R? E a) 2:1 b) 1:2 c) 4:1 d) 1:4 a)

d) four times

2R

R

67) A piece of copper wire (A) is at 50°C and another wire (B) of same material and dimensions is at 100°C. then a) A has higher resistivity b) B has higher resistivity c) Both have same resistivity d) None of the above 68) The resistance of an incandescent lamp is a) greater when switched off b) smaller when switched off c) greater when switched on d) same when switched on or off 69) A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R ′, then the ratio R/R ′ is – a) 1/25 b) 1/5 c) 5 d) 25 70) Which of the following terms does not represent electrical power in a circuit? 2 2 2 a) I R b) IR c) VI d) V /R 71) An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be a) 100 W b) 75 W c) 50 W d) 25 W 72) Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be a) 1:2 b) 2:1 c) 1:4 d) 4:1

200


Volume

Practical Skills

201

73) In an experiment to determine equivalent resistance of two resistors R1 and R2 in series, which of the following circuit diagrams shows the correct way of connecting the voltmeter in the circuit: (•)

I)

(•)

II)

A V

(•)

III)

V

(•)

A

IV)

A

V

V

A

a) I b) II c) III d) IV 74) To verify ohm’s law, Anil set up an arrangement as in ‘A; and Akhila set up an arrangement as in ‘B’. Which of them was correct? A)

– A +

B)

– V + +

A

–

+ V –

a) A b) B c) both A and B d) neither A nor B 75) Choose the wrong relationship 6 a) charge = current × time b) 1 kwh = 3.6 × 10 J c) Power = current × voltage d) 1 watt = 1 J 76) Household appliances are connected in a) Series b) parallel c) neither d) both 77) Which of the following is a series circuit of resistances? + V – + A – A)

+ V –

a) A

+ A –

B)

b) B

c) both A and B

d) neither A, B 4V

78) The current in the circuit is a) 4A b) 2.6 A c) 1A d) 3A

A

1Ω 2Ω 1Ω

79) The effective resistance between P and Q is (each resistor in the circuit is of 5Ω) 5 5 5 5 5 5 5 5 5 5 a) 20Ω b) 25Ω Q P 5 c) 5Ω d) 100Ω 5 5 5 5 5 5 5 5 5

80) If each resistance in the figure is of 9Ω. Then ammeter reading is 9V a) 5A b) 8A c) 2A d) 9A

A

81) The effective resistance between A and B

5 Ω 3 c) 15Ω a)

Volume

3 Ω 5 d) 5Ω

b)

5Ω A

E

F

5Ω

5Ω G


H

B

201

202

82) Four different measuring instruments are shown below. Out of these, the instrument that can be used for measuring current is/are the instruments labeled as I)

mA

Range 0–50 mA L.C = 1mA

II)

Range III) 0–3 V L.C = 0.1mV

V

a) I and III with I more reliable of the two c) II and III with II more reliable of the two

Range IV) 0–3 A L.C = 0.2mA

A

mV

Range 0–10 mV L.C = 0.1mv

b) I and IV with IV more reliable of the two d) II and IV with IV more reliable of the two

83) From the given readings, calculate the resistance a) 100Ω b) 200Ω –2 c) 10Ω d) 10 Ω

84) A student did the experiment to find the equivalent resistance, of two given resistors, R1 and R2, first when they are connected in series and next when they are connected in parallel. The two values of the equivalent resistance obtained by him were RS and RP respectively. He would find that, a) RS < RP b) RP < RS  R + R2   R + R2 d) RS = RP but not equal to  1 c) RS = RP =  1  2 2    85) Which of the given experimental set up is correct for determining the resistance of three resistances R1, R2, R3 in parallel

A

R1

R1 R2

I)

   equivalent

II)

R2 R3

V

R3

V

A

a) I b) II c) both d) neither 86) On plugging the key, the ammeter/ voltmeter is likely to be damaged in the circuit shown in figure ()

()

()

1)

2) V

v

()

3)

4) V A

A

a) 1 b) 2 c) 3 87) For the given circuits I and II, the ammeter readings would be V a) 2A in I and OA in II b) OA in I and 2A in II 3Ω c) 2A in I and 2A in II A d) OA in I and II

d) 4 V

A

6V I

88) Ohm’s law holds good for a) current through selenium c) current through carbon 202

A

3Ω

6V II

b) current through mercury d) none of the above


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89) Equivalent resistance between P and Q in the given circuit is P

a) 3R b) R/2 90) The resistors R1 and R2 are connected in R2

A)

A

Q

R

R

R

c) 2 R

d) R/3 V

R2

V

B)

R1

A

R1 ( )

( )

a) parallel in both b) Series in both c) parallel in ‘A’ and series in ‘B’ d) series in ‘A’ and parallel in ‘B’ 91) Two wires of the same material, and same area of cross section have length L and 2L and are connected in an electrical circuit in series. The ratio of their resistivity is a) 1:2 b) 2:1 c) 1:4 d) 1:1 92) 1 volt equals a) 1 Joule b) 1 Joule per coulomb c) 1 coulomb per metre d) 1 Newton per coulomb 93) How will the reading in the ammeter A be affected if another identical bulb Q is connected in parallel to P and the circuit is closed? The voltage in the mains is maintained at a constant value. Switch A a) The reading will be reduced to one–half b) The reading will not be affected Mains Q P c) The reading will be double the previous value d) The reading will be increased four–fold. 94) The SI unit of specific resistance is 2 –1 a) ohm m b) ohm m–1 c) ohm m d) (ohm) 95) Which two circuit components are connected in parallel in the following circuit diagram? V a) Rheostat and voltmeter b) Voltmeter and ammeter A c) Voltmeter and resistor d) Ammeter and resistor (•)

Volume


203

204

Answers to MCQs: Chapter 01: Chemical Reactions and Equations 1) a

2) b

3) b

4) b

5) a

6) b

7) c

8) b

9) c

10) b

11) a

12) d

13) a

14) b

15) d

16) a

17) b

18) c

19) c

20) d

21) b

Chapter 02: Acids, Bases and Salts 1) d

2) a

3) d

4) a

5) d

6) d

7) d

8) a

9) b

10) a

11) d

12) a

13) a

14) a

15) c

16) d

17) b

18) b

19) d

20) a

21) c

22) d

23) d

24) d

25) a

26) a

27) d

28) a

29) d

30) a

31) b

32) b

33) b

34) b

35) b

36) d

37) b

38) b

39) b

40) a

41) a

42) d

43) d

44) a

45) c

46) b

47) a

48) a

49) c

50) c

51) c

52) a

53) b

54) d

55) a

56) d

57) b

58) c

59) a

60) b

61) c

62) c

63) c

64) c

65) a

66) b

67) d

68) a

69) a

70) a

71) a

72) c

73) d

74) a

75) b

76) a

77) c

78) a

79) c

80) b

81) a

82) b

83) b

84) a

85) c

86) b

87) b

88) a

89) a

90) a

91) a

92) a

93) b

94) a

95) b

96) d

97) b

98) c

99) d

100) a

Chapter 03: Metals and Non–Metals 1) c

2) b

3) a

4) c

5) a

6) c

7) b

8) d

9) b

10) d

11) a

12) d

13) a

14) a

15) d

16) c

17) a

18) d

19) a

20) c

21) b

22) a

23) b

24) a

25) c

26) a

27) a

28) b

29) a

30) a

31) d

32) c

33) b

34) d

35) b

36) b

37) b

38) a

39) b

40) c

41) c

42) d

43) b

44) a

45) c

46) d

47) a

48) a

49) a

50) c

51) a

52) d

53) a

54) d

55) d

56) c

57) c

58) b

59) a

60) a

61) d

62) b

63) a

64) a

65) d

66) a

67) b

68) b

69) a

70) b

71) c

72) b

Chapter 06: Life Processes Preparation of Temporary Mount: 1) d

2) a

3) c

4) b

5) d

6) c

7) a

8) b

9) c

10) d

11) c

12) d

13) b

14) c

15) c

16) a

17) d

18) d

19) d

20) b

21) b

22) a

23) c

24) b

25) d

26) c

27) c

28) c

29) a

30) c

31) a

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Practical Skills

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Photosynthesis: 1) a

2) c

3) a

4) b

5) c

6) d

7) c

8) c

9) c

10) b

11) a

12) c

13) c

14) c

15) d

16) c

17) a

18) d

19) c

20) b

21) d

22) d

23) d

24) d

25) d

26) b

27) a

28) c

29) c

30) c

1) d

2) b

3) b

4) a

5) c

6) a

7) d

8) d

9) b

10) d

11) b

12) d

13) a

14) a

15) d

16) c

17) a

18) d

19) b

20) b

21) d

22) d

23) b

24) d

25) b

26) b

27) a

28) c

31) a

Respiration:

Absorption – Endosmosis in Raisins: 1) d

2) b

3) a

4) b

5) c

6) d

7) d

8) d

9) c

10) a

11) c

12) b

13) c

14) d

15) d

16) d

17) c

18) c

19) b

20) a

21) a

22) a

23) a

24) a

25) a

26) b

27) a

Chapter 12 & 13: Electricity and Magnetism 1) b

2) c

3) d

4) b

5) d

6) a

7) d

8) c

9) a

10) c

11) c

12) c

13) a

14) d

15) a

16) a

17) a

18) a

19) a

20) b

21) d

22) c

23) b

24) a

25) a

26) a

27) d

28) b

29) b

30) b

31) c

32) b

33) c

34) b

35) a

36) a

37) a

38) b

39) c

40) c

41) a

42) a

43) c

44) a

45) c

46) c

47) b

48) a

49) b

50) d

51) b

52) b

53) a

54) b

55) a

56) b

57) a

58) a

59) b

60) a

61) a

62) d

63) b

64) d

65) c

66) a

67) c

68) c

69) d

70) b

71) d

72) c

73) c

74) a

75) d

76) b

77) b

78) c

79) b

80) d

81) a

82) a

83) a

84) b

85) b

86) c

87) b

88) b

89) d

90) c

91) d

92) b

93) c

94) a

95) c

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X CBSE Science Tutorials

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