STOICHIOMETRY

PHYSICAL CHEMISTRY

STOICHIOMETRY

Digital Chemistry labs Pvt Ltd 403 Maha Laxmi Plaza Jawahar Nagar Kota (Raj.) Pin :- 324005 Phone :9929617387 Fax :0744 - 2405300 www.digitalchemistrylabs.com email:[email protected]

THE KEY The mole : The mole is the unit invented to provide a simple way of reporting the huge numbers the “massive heaps” of atoms and molecules in visible samples. It would be inconvenient to refer to large numbers like 2 ×1025 atoms, just as wholesalers would find it inconvenient to count individual items instead of dozens (12) or gross (144). 1 mole is number of atoms in exactly 12 gm of carbon – 12. One mole in broader terms applied to ions, molecules, electrons refer to 6.023 × 1023 of any objects also called as Avogadro number. so mole =

no.ofentitiesor objects 6.0231023

It is very big unit. For instance, 1mole of chemistry textbooks would cover the surface of the earth to a height of about 300 Km. While defining mole always state explicitly the identity of the particles to which the term moles refers. Mole-mass relation: 1 mole or gm object is molar mass of substance. For example 1 mole sodium refers to its molar mass 23 gm or 1 mol H2 refers to its molar mass 2 or 1 mole CO2 refers to its molar mass 44. mass of any substance mole = molar mass of substance

Average molar mass: Every element in nature exist along with its isotopes. So when we refers to molar mass, it means average molar mass i.e. Average molar mass =  % of isotope × molar mass of isotope. Mole volume relation: 1 mole means 22.4 litre of volume occupied by that entity at S.T.P. (0°C, 1 atm pressure) mole =

vol. of any substance at STP 22.4litre

Sometimes data is not given at STP, so we calculate no. of moles with the help of ideal gas equation

P1 V1 P2 V2 PV=nRT or calculate the volume under that condition with the help of relation T  T 1 2 *

We can convert any volume into mole by dividing it with 22.4 litre only when it is specified in the numerical at STP otherwise we can not.

*

Mole of any substance calculated are independent of temperature, pressure etc. because it represent amount of substance which is not going to change.

Mole - mass – volume relations: We can find the no. of atoms in 1 litre of any gas at STP by converting it through mol. So mole is standard unit through which you can find mass of any volume or volume for any mass at STP. Mole in compounds: 1 mole compound AxByCz refers to X mole of A, Y mole of B and Z mole of C entities. It can be ions for ionic compound or it can be atom in covalent compound . Digital Chemistry labs Pvt Ltd 403 Maha Laxmi Plaza Jawahar Nagar Kota (Raj.) Pin :- 324005 Phone :- 9929617387 Fax :- 0744 - 2405300

Stoichiometry Stoichiometry pronounced (“stoy – key – om – e – tree”) is the calculations of the quantities of reactants and products involved in a chemical reaction. This can be divided into two category. (A) Gravimetric analysis (B) Volumetric analysis (A) Gravimetric Analysis : In this we are concerned with calculations involving either (a) mass - mass relationship (b) mass-volume relationship (c) volume - volume relationship Method : If we know the balance chemical equations then we can adopt the simple mole method in which we relate reactants and products in their stoichiometric mol ratio. If we do not know balanced reactions we can adopt POAC (principle of atomic conversion) provided whole reactant is giving into product for which calculation is to be made. Limiting Reagent: It is very important concept in chemical calculation. It refers to reactant which is present in minimum stoichiometry quantity for a chemical reaction. It is reactant consumed fully in a chemical reaction. So all calculations related to various products or in sequence of reactions are made on the basis of limiting reagent. Percentage yield: Normally a reagent is associated with some impurity due to which actual yield of product is less than the theoretical maximum yield. actual yield The percentage yield of product = the theoretica l maximum yield  100

(B) Volumetric analysis : This mainly involve titrations based chemistry. It can be divided into two major category. (I) Non-redox system

(II) Redox system

(I) Non – redox system This involve following kind of titrations: 1. Acid-Base titrations 2. Back titration 3. Precipitation titration 4. Double indicator acid base titration Concentration terms : Volumetric calculations involves many concentration terms such as Mass * Density = Volume Density of any substance * Relative density = Density of refrence substance Digital Chemistry labs Pvt Ltd 403 Maha Laxmi Plaza Jawahar Nagar Kota (Raj.) Pin :- 324005 Phone :- 9929617387 Fax :- 0744 - 2405300

Density of any substance Density of water at 4C

*

Specific gravity =

*

Density of vapour at some temperature and pressure Vapour density = Density of H gas at same temperature and pressure 2

*

wt. of solute w %  = × 100 wt. of solution W

*

volume of solute v %   = volume of solution 100 V

*

wt. of solute w 100 %  = volume of solution V

*

Molarity(M) =

Mole of solute volume of solution in litre

*

Molality(m)

Mole of solute = wt . of solvent (in kg)

*

Let 1 mole solution contain x1 mole of solute & x2 mole of solvent. x1.

Molarity of solution (M) = x M  x M 1 1 2 2 where  = density of solution (g / L) M1 & M2 = Molar masses (g/mole) of solute & solvent respectively. x1

molality (m) = x . M × 1000 2 2 Relation between molarity (M) & Molality (m) :

M m =   M.M × 1000 1 *

Normality =

gm equivalent of solute volume of solution in litre

mole Where gm equivalent = n  factor

n factor is a conversion factor by which we can convert equivalents into mole or equivalent weight into molar mass or vice versa. Titrimetric Method of Analysis : A titrimetric method of analysis is based on chemical reaction such as. aA + tT  Product Where ‘a’ molecules of “analysis”, A, reacts with t molecules of reagent T. T is called Titrant normally taken in buret in form of solution of known concentration. The solution of Digital Chemistry labs Pvt Ltd 403 Maha Laxmi Plaza Jawahar Nagar Kota (Raj.) Pin :- 324005 Phone :- 9929617387 Fax :- 0744 - 2405300

titrant is called “standard solution”. The addition of titrant is added till the amount of T, chemically equivalent to that of ‘A’ has been added. It is said equivalent point of titration has been reached. In order to know when to stop addition of titrant, a chemical substance is used called indicator, which respond to appearance of excess of titrant by changing colour precisely at the equivalence point. The point in the titration where the indicator changes colour is termed the ‘end point’. It is possible that end point be as close as possible to the equivalence point. The term titration refer’s to process of measuring the volume of titrant required to reach the end point. For many years the term volumetric analysis was used rather than titrimetric analysis. However from a rigorons stand point the term titrimetric is preferable because volume measurement may not be confirmed to titration. In certain analysis, for example one might measure the volume of a gas. We can adopt mole method in balanced chemical reactions to relate reactant and products but it is more easier to apply law of equivalents in volumetric calculations because it does not require knowledge of balanced chemical reactions involved in sequence. Law of equivalents refers to that, equivalents of a limiting reactant is equal to equivalent of other reactant reacting in a chemical reaction or equal to equivalents of products formed in reaction. Balancing of chemical equation on the basis of n factor Whenever two substances react in such a way that their n factors are in the ratio of x : y, they would always react with each other in the molar ratio of y : x in a balanced chemical reaction. Acid-Base titration To find out strength or concentration of unknown acid or base it is titrated against base or acid of known strength. At the equivalence point we can know amount of acid or base used and then with the help of law of equivalents we can find strength of unknown. Meq of acid at equivalence point = Meq of base at equivalence point Back titration Back titration is used in volumetric analysis to find out excess of reagent added by titrating it with suitable reagent. It is also used to find out percentage purity of sample. For example in acid-base titration suppose we have added excess base in acid mixture. To find excess base we can titrate the solution with another acid of known strength. Precipitation titration : In ionic reaction we can know strength of unknown solution of salt by titrating it against a reagent with which it can form precipitate. For example NaCl strength can be known by titrating it against AgNO3 solution with which it form white ppt. of AgCl. So meq. of NaCl at equivalence point = meq of AgNO3 used = meq of AgCl formed Double indicator acid-base titration: In the acid-base titration the equivalence point is known with the help of indicator which changes its colour at the end point. In the titration of polyacidic base or polybasic acid there are more than one end point for each step neutralization. Sometimes one indicator is not able to give colour change at every end point. So to find out end point we have to use more than one indicator. For example in the titration of Na2CO3 against HCl there are two end points.

Digital Chemistry labs Pvt Ltd 403 Maha Laxmi Plaza Jawahar Nagar Kota (Raj.) Pin :- 324005 Phone :- 9929617387 Fax :- 0744 - 2405300

Na2CO3 + HCl  NaHCO3 + NaCl NaHCO3 + HCl  H2CO3 + NaCl When we use phenophthalein in the above titration it changes its colour at first end point when NaHCO3 is formed and with it we can not know second end point. Similarly with methyl orange it changes its colour at second end point only and we can not know first end point. It is because all indicator changes colour on the basis of pH of medium. So in titration of NaHCO3, KHCO3 against acid phenolphthalein can not be used. So we can write with phenolpthalein, if total meq of Na2CO3 = 1 then ½ meq of Na2CO3 = meq of HCl with methyl orange, meq of Na2CO3 = meq of HCl

*

Titration

Indicator

pH Range

n factor

Na2CO 3  against acid K 2 CO 3 

Phenolphthalein

8.3 – 10

1

Methyl orange

3.1 – 4.4

2

When we carry out dilution of solution, meq, milli mole or mole of substance does not change because they represent amount of substance.

Eudiometry : [For reactions involving gaseous reactants and products] *

The stoichiometric coefficient of a balanced chemical reactions also gives the ratio of volumes in which gasesous reactants are reacting and products are formed at same temperature and pressure. The volume of gases produced is often given by mentioning certain solvent which absorb contain gases. Solvent gas (es) absorb KOH CO2, SO2, Cl2 Ammonical Cu2Cl2 CO Turpentine oil O3 Alkaline pyrogallol O2 water NH3, HCl CuSO4 /CaCl2 H2O

*

Check out for certain assumption which are to be used for solving problem related to this.


THE ATLAS


EXERCISE-I Simple Application of Mole Concept Q.1

Chlorophyll, the green colouring matter of plants responsible for photosynthesis, contains 2.68% of magnesium by mass. Calculate the number of magnesium atoms in 2.00 g of chlorophyll.

Q.2

When 10.0g of marble chips (CaCO3) are treated with 50 mL of HCl (d = 1.096 g/mL, the marble dissolves, giving a solution and releasing CO2 gas. The solution weights 60.4 g. How many liters of CO2 gas are released ? The density of the gas is 1.798 g/L.

Q.3

105 mL water at 4°C is saturated with NH3 gas, producing a solution of d = 0.9 g/ml. If the solution contains 30% NH3 by wt. Calculate its volume.

Q.4

The atomic wt. of A and B are 20 and 40. If x gm of A contains Y atoms, how many atoms are present in 2 x g of B.

Q.5

Density of a gas relative to air is 1.17. Find the mol. mass of the gas. [Mair = 29g/mol]

Q.6

Sodium chloride has a density of 2.165 g cm3 at 25°C. Calculate the no. of atoms in 1.000 cm3 of sodium chloride at 25°C.

Q.7

A chemist puts 5 gm of a mixture of NO2 & N2O4 into a large bulb. If the sample was 50% of each by wt., how many moles of each gas are in the bulbs.

Q.8

Caffeine burns in O2 to give CO2, H2O & NO2. How many gms of O2 are required and how many gms of NO2 would be produced from burning 1.0g Caffeine. The reaction of caffeine with oxygen is written as follows: 2C8H10N4O2 + 27O2  16CO2 + 10H2O + 8NO2

Q.9

Equal weights of mercury and I2 are allowed to react completely to form a mixture of mercurous and mercuric iodide leaving none of the reactants. Calculate the ratio of the wts of Hg2I2 and HgI2 formed. Concept of limiting reagents

Q.10

Titanium, which is used to make air plane engines and frames, can be obtained from titanium tetrachloride, which in turn is obtained from titanium oxide by the following process : 3 TiO2(s) + 4C (s) + 6Cl2 (g)  3TiCl4(g) + 2CO2(g) + 2CO (g) A vessel contains 4.15 g TiO2, 5.67 g C and; 6.78 g Cl2, suppose the reaction goes to completion as written, how many gram of TiCl4 can be produced ? (Ti = 48)

Q.11

A chemist wants to prepare diborane by the reaction 6 LiH + 8BF3  6Li BF4 + B2H6 If he starts with 2.0 moles each of LiH & BF3. How many moles of B2H6 can be prepared.

Q.12

When you see the tip of a match fire , the chemical reaction is likely to be P4S3 + 8O2  P4O10 + 3SO2 What is the minimum amount of P4S3 that would have to be burned to produce at least 1.0 g of P4O10 and at least 1.0 g of SO2


Empirical and Molecular Formulae Q.13

10 5 B

and 11 5 B are two isotopes of boron. If average mass number is 10.2. What is the % of each.

Q.14

Tha action of bacteria on meat and fish produces a poisonus compound called cadaverine. It is 58.77% C, 13.81% H, and 27.42% N. Its molar mass is 102 g/mol. Determine the molecular formula of cadaverine.

Q.15

On combustion analysis, a 0.450 g sample of Caproic acid (contained only C,H & O) gives 0.418 g of H2O and 1.023 g of CO2. What is the empirical formula of Caproic acid? If the molecular mass of Caproic acid is 116 amu, what is the molecular formula? Atomic Weight

Q.16

A sample of metallic element X, weighs 4.315g combines with 0.4810L of Cl2 gas (at normal pressure and 20°C) to form the metal chloride XCl. If the density of Cl2 gas under these conditions is 2.948 g/L. What is the mass of the chlorine? The at. wt. of chlorine is 35.45 amu. What is at wt of X, what is identifyof X.

Q.17

A sample of pure metal M weighing 1.35g was quantitatively converted into 1.88g of pure MO. Calculate at wt. of metal M

Q.18

Cu2S and M2S are isomorphous. The % of S in former is 20.14 and in the later 12.94. At wt of Cu = 63.57. Calculate at wt of M.

Q.19

A compound which contains one atom of X and two atoms of Y for each three atoms of Z is made by mixing 5.00 g of X, 1.15 × 1023 atoms of Y and 0.03 mole of Z atoms. Given that only 4.40 g of compound results. Calculate the atomic weight of Y if the atomic weights of X and Z are 60 and 80 amu respectively. Gravimetric Method of Analysis

Q.20

A 0.6025 gm sample of a chloride salt was dissolved in water and the chloride precipitated by adding excess silver nitrate. The precipitate of silver chloride was filtered, washed, dried, and found to weigh 0.7134 gm. Calculate the percentage of chloride (Cl) in the sample.

Q.21

A 0.4852 gm sample of iron ore is dissolved in acid, the iron oxidized to the +3 state, and then precipitated as the hydrous oxide, Fe2O3 · xH2O. The precipitate is filtered, washed, and ignited to Fe2O3, which is found to weigh 0.2481 gm. Calculate the percentage of iron (Fe) in the sample.

Q.22

The phosphorous in a sample of phosphate rock weighing 0.5428 gm is precipitated as MgNH4PO4 · 6H2O and ignited to Mg2P2O7. If the ignited precipitate weighs 0.2234 gm, calculate the percentage of P2O5 in the sample and the percent purity expressed as P rather than P2O5.

(a) (b) Q.23

Calculate the number of milliliters of ammonia, density 0.99 g/ml, 2.3% by weigh NH3, which will be required to precipitate as Fe(OH)3 the iron in a 0.70 gm sample that contain 25% Fe2O3.

Q.24

What size sample which contains 12.0% chlorine (Cl) should be taken for analysis if the chemist wishes to obtain a precipitate of AgCl which weighs 0.50 gm?


Q.25

A 0.75 gm sample containing both NaCl and NaBr is titrated with 0.1043 M AgNO3, using 42.23ml. A second sample of the same weight is treated with excess silver nitrate, and the mixture of AgCl and AgBr is filtered, dried and found to weigh 0.8042 gm. Calculate the percentages of NaCl and NaBr in the sample.

Q.26

A mineral consists of an equimolar mixture of the carbonates of two bivalent metals. One metal is present to the extent of 13.2% by weight. 2.58 g of the mineral on heating lost 1.233 g of CO2. Calculate the % by weight of the other metal.

Q.27

Determine the percentage composition of a mixture of anhydrous sodium carbonate and sodium bicarbonate from the following data: wt. of the mixture taken = 2g Loss in weight on heating = 0.124 g.

Q.28

A 10 g sample of a mixture of calcium chloride and sodium chloride is treated with Na2CO3 to precipitate calcium as calcium carbonate. This CaCO3 is heated to convert all the calcium to CaO and the final mass of CaO is 1.62g. Calculate % by mass of NaCl in the original mixture. Concentration terms

Q.29

The density of a solution containing 13% by mass of sulphuric acid is 1.09 g/mL. Calculate the molarity of the solution.

Q.30

The mole fraction of CH3OH in an aqueous solution is 0.02 and its density is 0.994 g cm–3. Determine its molarity and molality.

Q.31

The density of a solution containing 40% by mass of HCl is 1.2 g/mL. Calculate the molarity of the solution.

Q.32

15 g of methyl alcohol is present in 100 mL of solution. If density of solution is 0.90 g mL–1. Calculate the mass percentage of methyl alcohol in solution.

Q.33

Units of parts per million (ppm) or per billion (ppb) are often used to describe the concentrations of solutes in very dilute solutions. The units are defined as the number of grams of solute per million or per billion grams of solvent. Bay of Bengal has 1.9 ppm of lithium ions. What is the molality of Li+ in this water ?

Q.34

Find out the volume of 98% w/w H2SO4 (density = 1.8 gm/ ml) must be diluted to prepare 12.5 litres of 2.5 M sulphuric acid solution.

Q.35

10 ml of pure ethanol (d = 0.785g/ml) is diluted with water to a volume of 100ml. Find molarity.

Q.36

Calculate molality of aq. H2SO4 containing 61% by wt. of H2SO4. The density of solution is 1.5091 g/cc.

Q.37

3.2665 gm of H3PO4 are present in one litre of a solution. Find normality.

Q.38

In what ratio should you mix 0.2M NaNO3 and 0.1M Ca(NO3)2 solution so that in resulting solution, the concentration of negative ion is 50% greater than conc. of positive ion. A 500 ml solution was prepared by dissolving 28.5 gm of MgCl2 in water. If the density of MgCl2 solution is 1.2 gm/ml, calculate Molarity of Cl– ion Mole fraction of Mg2+ ion Concentration in ppm of Mg2+ ion

Q.39 (a) (b) (c)


Acid Base Titration Q.40

How many ml of 0.1 N HCl are required to react completely with 1 g mixture of Na2CO3 and NaHCO3 containing equimolar amounts of two?

Q.41

0.5 g of fuming H2SO4 (oleum) is diluted with water. The solution requires 26.7 ml of 0.4 N NaOH for complete neutralization. Find the % of free SO3 in the sample of oleum.

Q.42

H3PO4 is a tri basic acid and one of its salt is NaH2PO4. What volume of 1 M NaOH solution should be added to 12 g of NaH2PO4 to convert it into Na3PO4?

Q.43

1.64 g of a mixture of CaCO3 and MgCO3 was dissolved in 50 mL of 0.8 M HCl. The excess of acid required 16 mL of 0.25 M NaOH for neutralization. Calculate the percentage of CaCO3 and MgCO3 in the sample.

Q.44

1.5 g of chalk were treated with 10 ml of 4N – HCl. The chalk was dissolved and the solution made to 100 ml 25 ml of this solution required 18.75 ml of 0.2 N – NaOH solution for complete neutralisation. Calculate the percentage of pure CaCO3 in the sample of chalk? Double titration

Q.45

A solution contains Na2CO3 and NaHCO3. 20ml of this solution required 4ml of 1N – HCl for titration with Ph indicator. The titration was repeated with the same volume of the solution but with MeOH. 10.5 ml of 1 – N HCl was required this time. Calculate the amount of Na2CO3 & NaHCO3.

Q.46

A solution contains a mix of Na2CO3 and NaOH. Using Ph as indicator 25ml of mix required 19.5 ml of 0.995 N HCl for the end point. With MeOH, 25 ml of the solution required 25ml of the same HCl for the end point. Calculate gms/L of each substance in the mix .

Q.47

200ml of a solution of mixture of NaOH and Na2CO3 was first titrated with Ph and

Q.48

A solution contains Na2CO3 and NaHCO3. 10ml of this requires 2ml of 0.1M H2SO4 for neutralisation using Ph indicator. MeOH is then added when a further 2.5 ml of 0.2 M H2SO4 was needed. Calculate strength of Na2CO3 and NaHCO3 in g/L.

N HCl. 17.5 ml of 10 HCl was required for end point. After this MeOH was added and 2.5 ml of some HCl was again required for next end point. Find out amounts of NaOH and Na2CO3 in the mix.


Redox Titration Q.49

It requires 40.05 ml of 1M Ce4+ to titrate 20ml of 1M Sn2+ to Sn4+. What is the oxidation state of the cerium in the product.

Q.50

A volume of 12.53 ml of 0.05093 M SeO2 reacted with exactly 25.52 ml of 0.1M CrSO4. In the reaction, Cr2+ was oxidized to Cr3+. To what oxidation state was selenium converted by the reaction.

Q.51

Potassium acid oxalate K2C2O4 · 3H2C2O4·4H2O can be oxidized by MnO4– in acid medium. Calculate the volume of 0.1M KMnO4 reacting in acid solution with one gram of the acid oxalate.

Q.52

Metallic tin in the presence of HCI is oxidized by K2Cr2O7 to stannic chloride, SnCl4. What volume of deci-normal dichromate solution would be reduced by 1g of tin.

Q.53

5g sample of brass was dissolved in one litre dil. H2SO4. 20 ml of this solution were mixed with KI, liberating I2 and Cu+ and the I2 required 20 ml of 0.0327 N hypo solution for complete titration. Calculate the percentage of Cu in the alloy.

Q.54

0.84 g iron ore containing x percent of iron was taken in a solution containing all the iron in ferrous condition. The solution required x ml of a dichromatic solution for oxidizing the iron content to ferric state. Calculate the strength of dichromatic solution. The neutralization of a solution of 1.2 g of a substance containing a mixture of H2C2O4. 2H2O, KHC2O4. H2O and different impurities of a neutral salt consumed 18.9 ml of 0.5 N NaOH solution. On titration with KMnO4 solution, 0.4 g of the same substance needed 21.55 ml of 0.25 N KMnO4. Calculate the % composition of the substance.

Q.55

Back Titration Q.56

50gm of a sample of Ca(OH)2 is dissolved in 50ml of 0.5N HCl solution. The excess of HCl was titrated with 0.3N – NaOH. The volume of NaOH used was 20cc. Calculate % purity of Ca(OH)2.

Q.57

One gm of impure sodium carbonate is dissolved in water and the solution is made up to 250ml. To 50ml of this made up solution, 50ml of 0.1N – HCl is added and the mix after shaking well required 10ml of 0.16N – NaOH solution for complete titration. Calculate the % purity of the sample.

Q.58

What amount of substance containing 60% NaCl, 37% KCl should be weighed out for analysis so that after the action of 25 ml of 0.1N AgNO3 solution, excess of Ag+ is back titrated with 5 ml of NH4SCN solution? Given that 1 ml of NH4SCN = 1.1 ml of AgNO3.

Q.59

5g of pyrolusite (impure MnO2) were heated with conc. HCl and Cl2 evolved was passed through N excess of KI solution. The iodine liberated required 40 mL of hypo solution. Find the % of MnO2 in 10 the pyrolusite.


Eudiometry Q.60

10 ml of a mixture of CO, CH4 and N2 exploded with excess of oxygen gave a contraction of 6.5 ml. There was a further contraction of 7 ml, when the residual gas treated with KOH. What is the composition of the original mixture?

Q.61

When 100 ml of a O2 – O3 mixture was passed through turpentine, there was reduction of volume by 20 ml. If 100 ml of such a mixture is heated, what will be the increase in volume? [Hint : O3 is absorbed by turpentine]

Q.62

10 ml of a gaseous organic compound containing C, H and O only was mixed with 100 ml of oxygen and exploded under conditions which allowed the water formed to condense. The volume of the gas after explosion was 90 ml. On treatment with potash solution, a further contraction of 20 ml in volume was observed. Given that the vapour density of the compound is 23, deduce the molecular formula. All volume measurements were carried out under the same conditions.

Q.63

A mixture of formic acid and oxalic acid is heated with concentrated H2SO4. The gas produced is collected and on its treatment with KOH solution the volume of the gas decreased by one-sixth. Calculate the molar ratio of the two acids in the original mixture.

Q.64

40 ml of a mixture of hydrogen, CH4 and N2 was exploded with 10 ml of oxygen. On cooling, the gases occupied 36.5 ml. After treatment with KOH the volume reduced by 3 ml and again on treatment with alkaline pyrogallol, the volume further decreased by 1.5 ml. Determine the composition of the mixture.

Q.65

5 ml of a gaseous hydrocarbon was exploded to 30 ml of O2. The resultant gas, on cooling is found to measure 25 ml of which 10 ml are absorbed by KOH and the remainder by pyragallal. Determine molecular formula of hydrocarbon.


PROFICIENCY TEST Q.1

Fill in the blanks with appropriate items :

1.

The number of water molecules in 0.5 mol of barium chloride dihydrate is _________.

2.

20ml of 0.1 M H2C2O4 · 2H2O (oxalic acid) solution contains oxalic acid equal to _________ moles.

3.

The volume of 1.204 × 1024 molecules of water at 4°C is _________.

4.

0.2 mol of ozone (O3) at N.T.P. will occupy volume _________ L.

5.

The balancing of chemical equation is based upon _________.

6.

2 gm of hydrogen will have same number of H atoms as are there in ________ g hydrazine (NH2–NH2).

7.

The mass of x atoms of element =

8.

The moles of x atoms of a triatomic gas =

9.

The amount of Na2SO4 which gives 9.6 gm of SO 24  is _________.

10.

The 44 mg of certain substance contain 6.02 × 1020 molecules. The molecular mass of the substance is _________.

11.

The mass of 1 ×1022 molecules of CuSO4. 5H2O is _________.

12.

The atomic mass of iron is 56. The equivalent mass of the metal in FeCl2 is ___________ and that in FeCl3 is _________.

13.

The sulphate of a metal M contains 9.87% of M. The sulphate is isomorphous with ZnSO4.7H2O. The atomic mass of M is __________.

14.

A binary compound contains 50% of A (at. mass = 16) & 50% B (at. mass = 32). The empirical formula of the compound is _________.

15.

10.6 g of Na2CO3 react with 9.8 g of H2SO4 to form 16 g of Na2SO4 & 4.4 g CO2. This is in accordance with the law of _________.

16.

3 g of a salt (m. wt. 30) are dissolved in 250 ml of water. The molarity of solution is _________.

17.

0.5 mole of BaCl2 are mixed with 0.2 mole of Na3PO4 the maximum number of mole of Ba3(PO4)2 formed are __________.

18.

The Eq. weight of Na2HPO4 (base) is ______________.

.........x NA . x × _________. NA


19.

The mole fraction of solute in 20% (by weight) aqueous H2O2 solution is __________.

20.

A metallic oxide contains 60% of the metal. The Eq. weight of the metal is __________.

21.

The number of gm of anhydrous Na2CO3 present in 250 ml of 0.25 N solution is___________.

22.

________ ml of 0.1 M H2SO4 is required to neutralize 50 ml of 0.2 M NaOH solution.

23.

The number of mole of water present in 90 g H2O are _________.

24.

The concentration of K+ ion in 0.2 M K2Cr2O7 solution would be__________.

25.

280 ml of sulphur vapour at NTP weight 3.2 g . The Mol. formula of the sulphur vapour is ______.

Q.2

True or False Statements :

1.

Equal volumes of helium and nitrogen under similar conditions have equal number of atoms.

2.

The smallest particle is a substance which is capable in independent existence is called an atom.

3.

The number of formula units in 0.5 mole of KCl is 6.02 × 1023.

4.

22.4 L of ethane gas at S.T.P. contains H atoms as are present in 3 gram molecules of dihydrogen.

5.

Molarity of pure water is 55.5.

6.

A 20% solution of KOH (density = 1.02 g/ml) has molarity = 3.64.

7.

In a mixture of 1 g C6H6 & 1 g C7H8, the mole fraction of both are same.

8.

1 mole of C12H22O11 contains 22 hydrogen atoms.

9.

KClO4 & KMnO4 are isomorphous in nature.

10.

Mass of 3.01 × 1023 molecules of of methane is 8 gm.

11.

A hydrocarbon contains 86% C. 448 ml of the hydrocarbon weighs 1.68 g at STP. Then the hydrocarbon is an alkene.

12.

6.023 × 1054 e–s weigh one kg.

13.

An oxide of metal M has 40% by mass of oxygen. Metal M has relative atomic mass of 24. The empirical formula of the oxide is MO.

14.

5 g of a crystalline salt when rendered anhydrous lost 1.8 g of water. The formula weight of the anhydrous salt is 160. The number of molecules of water of crystallisation in the salt is 5. Digital Chemistry labs Pvt Ltd 403 Maha Laxmi Plaza Jawahar Nagar Kota (Raj.) Pin :- 324005 Phone :- 9929617387 Fax :- 0744 - 2405300

15.

Number of valence e–s in 4.2 g of N 3– is 24 NA.

16.

The equivalent mass of KMnO4 in alkaline medium is molar mass divided by five.

17.

The equivalent mass of Na2S2O3 in its reaction with I2 is molar mass divided by two.

18.

In a reaction, H2MoO4 is changed to MoO2+. In this case, H2MoO4 acts as an oxidising agent.

19.

KBrO3 acts as a strong oxidising agent. It accepts 6 electrons to give KBr.

20.

0.1 M sulphuric acid has normality of 0.05 N.

21.

The reaction, 2H2O2  2H2O + O2 is not an example of a redox reaction.

22.

The disproportionation reaction, 2Mn3+ + 2H2O  MnO2 + Mn+2 + 4H+ is an example of a redox reaction.

23.

The oxidation number of hydrogen is always taken as + 1 in its all compounds.

24.

The increase in oxidation number of an element implies that the element has undergone reduction.

25.

The oxidation state of oxygen atom in potassium super oxide is  1 . 2


EXERCISE-II Q.1

A sample of calcium carbonate contains impurities which do not react with a mineral acid. When 2 grams of the sample were reacted with the mineral acid, 375 ml of carbon dioxide were obtained at 27°C and 760 mm pressure. Calculate the % purity of the sample of CaCO3?

Q.2

One gram of an alloy of aluminium and magnesium when heated with excess of dil. HCl forms magnesium chloride, aluminium chloride and hydrogen. The evolved hydrogen collected over mercury at 0°C has a volume of 1.2 litres at 0.92 atm pressure. Calculate the composition of the alloy.

Q.3

Chloride samples are prepared for analysis by using NaCl, KCl, NH4Cl separately or as mixtures. What minimum volume of a 5% (by weight) AgNO3 solution (sp. gr = 1.04) must be added to a sample weighing 0.3 g in order to ensure complete precipitation of chloride in every possible case?

Q.4

Sulfur dioxide is an atmospheric pollutant that is converted to sulfuric acid when it reacts with water vapour. This is one source of acid rain, one of our most pressing environmental problems. The sulfur dioxide content of an air sample can be determined as follows. A sample of air is bubbled through an aqueous solution of hydrogen peroxide to convert all of the SO2 to H2SO4 H2O2 + SO2  H2SO4 Titration of the resulting solution completes the analysis. In one such case, analysis of 1550 L of Los Angeles air gave a solution that required 5.70 ml of 5.96 × 10–3M NaOH to complete the titration. Determine the number of grams of SO2 present in the air sample.

Q.5

In a water treatment plant, Cl2 used for the treatment of water is produced from the following reaction 2KMnO4 + 16 HCl  2KCl + 2MnCl2 + 8H2O + Cl2. If during each feed 1 l KMnO4 having 79% (w/v) KMnO4 & 9 l HCl with d = 1.825 gm/ ml & 10% (w/w) HCl are entered & if that percent yield is 80% then calculate amount of Cl2 produced. amount of water that can be treated by Cl2 if 1 litres consumes 28.4 g of Cl2 for treatment. vol. of water treated Calculate efficiency  of the process if  = vol of total feed

(a) (b) (c) Q.6

A 2.0 g sample of a mixture containing sodium carbonate, sodium bicarbonate and sodium sulphate is heated till the evolution of CO2 ceases. The volume of CO2 at 750 mmHg pressure and at 298 K is measured to be 123.9 mL. A 1.5 g of the sample requires 150 mL of M /10 HCl for complete neutralization. Calculate the percentage composition of the components of the mixture.

Q.7

3.6 g of Mg is burnt in limited supply of oxygen. The residue was treated with 100 mL of H2SO4 (35% by mass,1.26 g mL–1 density). When 2.463 L of H2 at 760 mm Hg at 27°C was evolved. After the reaction, H2SO4 was found to have a density of 1.05 g mL–1. Assuming no volume change in H2SO4 solution. Find (i) % by mass of final H2SO4 (ii) % by mass of Mg converted to oxide (iii) mass of oxygen used. (Mg = 24, S= 32)


Q.8

One mole of a mixture of N2, NO2 and N2O4 has a mean molar mass of 55.4. On heating to a temperature at which all the N2O4 may be pressured to have dissociated : N2O4  2NO2, the mean molar mass tends to the lower value of 39.6. What is the mole ratio of N2 : NO2 : N2O4 in the original mixture?

Q.9

A mixture of FeO and Fe2O3 is reacted with acidified KMnO4 solution having a concentration of 0.2278 M, 100 ml of which was used. The solution was then titrated with Zn dust which converted Fe3+ of the solution to Fe2+. The Fe2+ required 1000 ml of 0.13 M K2Cr2O7 solution. Find the % of FeO & Fe2O3.

Q.10

50ml of a solution, containing 1gm each Na2CO3, NaHCO3 and NaOH was titrated with N-HCl. What will be the titre readings if (a) only Ph is used as indicator. (b) only MeOH is used as indicator from the beginning. (c) MeOH is added after the first end point with Ph.

Q.11

A 0.517g sample containing Ba(SCN)2 was dissolved in a bicarbonate solution. 50.0 mL of 0.107 N iodine was added, and the mixture was allowed to stand for five minutes. The solution was then acidified, and the excess I2 was titrated with 16.3 mL of 0.0965 M sodium thiosulphate. Calculate the percent Ba(SCN)2 in the sample.

Q.12

A mixture of Xe and F2 was heated. A sample of white solid thus formed reacted with H2, to give 81 ml of Xe at STP and HF formed required 68.43 ml of 0.3172 M NaOH for complete neutralization. Determine empirical formula.

Q.13

Chrome alum K2SO4 . Cr2(SO4)3 . 24 H2O is prepared by passing SO2 gas through an aqueous solution of K2Cr2O7 acidified with dilute sulphuric acid till the reduction is complete. The alum is crystallized followed by filtration/centrifugation. If only 90% of the alum can be recovered from the above process, how much alum can be prepared from 10kg of K2Cr2O7? Give the number of moles of electrons supplied by SO2 for reducing one mole of K2Cr2O7.

Q.14

A substance of crude copper is boiled in H2SO4 till all the copper has reacted. The impurities are inert to the acid. The SO2 liberated in the reaction is passed into 100 mL of 0.4 M acidified KMnO4. The solution of KMnO4 after passage of SO2 is allowed to react with oxalic acid and requires 23.6 mL of 1.2 M oxalic acid. If the purity of copper is 91%, what was the weight of the sample.

Q.15

25 mL of a solution containing HCl was treated with excess of M/5 KIO3 and KI solution of unknown concentration where I2 liberated is titrated against a standard solution of 0.021M Na2S2O3 solution whose 24 mL were used up. Find the strength of HCl and volume of KIO3 solution consumed.

Q.16

A 10g sample of only CuS and Cu2S was treated with 100 mL of 1.25 M K2Cr2O7. The products obtained were Cr3+, Cu2+ and SO2. The excess oxidant was reacted with 50 mL of Fe2+ solution. 25 ml of the same Fe2+ solution required 0.875M acidic KMnO4 the volume of which used was 20 mL. Find the % of CuS and Cu2S in the sample.

Q.17

H2O2 is reduced rapidly by Sn2+, the products being Sn4+ & water. H2O2 decomposes slowly at room temperature to yield O2 & water. Calculate the volume of O2 produced at 20C & 1.00 atm when 200g of 10.0 % by mass H2O2 in water is treated with 100.0 ml of 2.00 M Sn2+ & then the mixture is allowed to stand until no further reaction occurs. Digital Chemistry labs Pvt Ltd 403 Maha Laxmi Plaza Jawahar Nagar Kota (Raj.) Pin :- 324005 Phone :- 9929617387 Fax :- 0744 - 2405300

Q.18

Q.19

A sample of steel weighing 0.6 gm and containing S as an impurity was burnt in a stream of O2, when S was converted to its oxide SO2. SO2 was then oxidized to SO4– – by using H2O2 solution containing 30ml of 0.04 M NaOH. 22.48 ml of 0.024 M HCl was required to neutralize the base remaining after oxidation. Calculate the % of S in the sample. CuFeS2 mineral was analysed for Cu and Fe percentage. 10g of it was boiled with dil. H2SO4 and diluted to 1L. 10 mL of this solution required 2mL of 0.01M MnO4 in acidic medium. In another titration 25 mL of the same solution required 5 mL of 0.01M S2O32 solution iodometrically. Calculate percentage of Cu and Fe in the mineral.

Q.20

A 10gm mixture of Cu2S and CuS was treated with 200 ml of 0.75 M MnO4– in acid solution, producing SO2, Cu2+ & Mn2+. The SO2 was boiled off and the excess MnO4– was titrated with 175 ml of 1M Fe2+ solution. Calculate the % CuS in the original mixture.

Q.21

3.3 gm of a sample of Anhydrous CuSO4 was dissolved in water and made to 250ml. 25 ml of this solution after taking usual precautions was treated with a little excess of KI solution. A white ppt. of Cu2I2 and iodine was evolved. The iodine so evolved required 24.6 ml of hypo solution containing 20gm of (Na2S2O3 · 5H2O) per litre. What is the purity of CuSO4 solution. 1.16 g CH3(CH2)n COOH was burnt in excess air and the resultant gases (CO2 and H2O) were passed through excess NaOH solution. The resulting solution was divided in two equl parts. One part requires 50 mL of 1 N HCl for neutralization using phenolphthalein as indicator. Another part required 80 mL of 1N HCl for neutralization using methyl orange as indicator. Find the value of n and the amount of excess NaOH solution taken initially.

Q.22

Q.23

Q.24

Q.25

A 1.65 gm sample of FeS2 was oxidized by excess oxygen & the products were SO2 and Fe2+. The SO2 gas produced was passed through an acidified solution of 40ml Ba(MnO4)2 produced SO4– – & Mn2+. The excess permagnate was diluted to 100 ml & 10 ml of it was treated with excess KI & iodine produced req. 0.05 M 5 ml hypo solution producing S4O62–. In a separate titration the 25 ml of same solution of permagnate under alkaline condition when treated with KI produced I2 that required 20 ml of 0.05 M hypo solution producing S4O62– & Mn6+. Calculate the % of FeS2 in the sample. Reducing sugars are sometimes characterized by a number RCu, which is defined as the number of mg of copper reduced by 1 gm of sugar, in which half reaction for the copper is Cu2+ + OH–  Cu2O + H2O It is sometimes more convenient to determine the reducing power of a carbohydrate by an indirect method. In this method 43.2 mg of the carbohydrate was oxidized by an excess of K3(Fe(CN)6). The Fe(CN)64– formed in this reaction required 5.29 ml of 0.0345 N Ce(SO4)2 for reoxidation to Fe(CN)63. Determine the RCu value for the sample. 2g of chromite ore sample was mixed with enough potassium carbonate and potassium chlorate and fused. The reaction that occurred was: 6FeCr2O4 + 12K2CO3 + 7KCIO3  3Fe2O3 + 12 K2CrO4 + 7KCl + 12CO2 The fused mass was cooled and extracted with 2N sulphuric acid. This was filtered and thoroughly washed. The filterate and washings were collected in a 500 ml. Volumetric flask. When all the soluble portion of the fused mass was extracted, 100 ml of 1M solution of ferrous ammonium sulphate were added and the solution made to 500ml. An aliquot of 25ml was titrated with potassium dichromate solution, prepared by dissolving 0.98 g of dried potassium dichromate in distilled water in a 250ml volumetric flask. The titration required 32.5 ml of this solution. Calculate the percentage of chromium in the sample of the ore. Digital Chemistry labs Pvt Ltd 403 Maha Laxmi Plaza Jawahar Nagar Kota (Raj.) Pin :- 324005 Phone :- 9929617387 Fax :- 0744 - 2405300

EXERCISE-III Q.1

Which has maximum number of atoms of oxygen (A) 10 ml H2O(l) (B) 0.1 mole of V2O5 (C) 12 gm O3(g) (D) 12.044 ×1022 molecules of CO2

Q.2

Mass of one atom of the element A is 3.9854 × 10 –23g. How many atoms are contained in 1 g of the element A? (A) 2.509 × 1023 (B) 6.022 × 1023 (C) 12.044 ×1023 (D) None

Q.3

The total no. of electrons present in 11.2 litre of NH3 at STP are (A) 6.022 × 1023 (B) 3.011 × 1023 (C) 3.011 × 1024

Q.4

Q.5

1 gm-atom of nitrogen represents : (A) 6.02 × 1023 N2 molecules (C) 11.2 lit. of N2 at N.T.P.

(D) None

(B) 22.4 lit. of N2 at N.T.P. (D) 28 g of nitrogen

Al2(SO4)3. x H2O has 8.20 % aluminium by mass. The value of x is (A) 4 (B) 10 (C) 16

(D) 18

Q.6

If average molecular wt. of air is 29, then assuming only N2 and O2 gases are there which options are correct regarding composition of air (i) 75% by mass of N2 (ii) 75% by moles N2 (iii) 72.41% by mass N2 (A) only (i) is correct (B) only (ii) is correct (C) both (ii) and (iii) are correct (D) both (i) and (ii) are correct

Q.7

A spherical ball of radius 3 cm contains 66.66 % iron. If density is 1.5 g/cm3, number of mole of Fe present approximately is: (A) 1 (B) 2 (C) 20 (D) None

Q.8

Density of dry air containing only N2 and O2 is 1.146 gm/lit at 740 mm and 300 K. What is % composition of N2 by weight in the air. (A) 78% (B) 82% (C) 73.47% (D) 72.42%

Q.9

What is the number of moles of Fe(OH)3 that can be produced by allowing 1 mole of Fe2S3, 2 mole of H2O and 3 mole of O2 to react 2Fe2S3 + 6H2O + 3O2  4Fe(OH)3 + 6S (A) 2 (B) 1.34 (C) 3.52 (D) none

Q.10

What percentage of phosphorus (P) is present in the compound CaCO3. 3Ca3(PO4)2? (A) 18% (B) 45.36% (C) 28.61% (D) 15.12%

Q.11

A gaseous mixture of H2 and NH3 gas contains 68 mass % of NH3. The vapour density of the mixture is (A) 6.1 (B) 5 (C) 2.5 (D) None of these

Q.12

A sample of ammonium phosphate, (NH4)3 PO4, contains 3.18 mol of hydrogen atoms.The number of moles of oxygen atoms in the sample is : (A) 0.265 (B) 0.795 (C) 1.06 (D) 3.18 Digital Chemistry labs Pvt Ltd 403 Maha Laxmi Plaza Jawahar Nagar Kota (Raj.) Pin :- 324005 Phone :- 9929617387 Fax :- 0744 - 2405300

Q.13

Q.14

12 litre of H2 and 11.2 litre of Cl2 are mixed and exploded. The composition by volume of mixture is (A) 24 litre of HCl (B) 0.8 litre Cl2 and 20.8 lit HCl (C) 0.8 litre H2 & 22.4 litre HCl (D) 22.4 litre HCl Weight of oxygen in Fe2O3 and FeO is in the simple ratio for the same amount of iron is (A) 3 : 2 (B) 1 : 2 (C) 2 : 1 (D) 3 : 1

Q.15

A mixture of gas ''X'' (mol. wt. 16) and gas Y (mol. wt. 28) in the mole ratio a : b has a mean molecular weight 20. What would be mean molecular weight if the gases are mixed in the ratio b : a under identical conditions (gases are non reacting). (A) 24 (B) 20 (C) 26 (D) 40

Q.16

A mixture of CuO and Cu2O contain 88% Cu. What is the percentage of CuO present in the mixture? (A) 91.35% (B) 8.89% (C) 18.9% (D) 20%

Q.17

Consider the following nuclear reactions involving X & Y. X  Y + 42 He Y  8O18 + 1H1 If both neutrons as well as protons in both the sides are conserved in nuclear reaction then identify period number of X & moles of neutrons in 4.6 gm of X (A) 3, 2.4 NA (B) 3, 2.4 (C) 2, 4.6 (D) 3, 0.2 NA

Q.18

To 500 ml of 2 M impure H2SO4 sample, NaOH solution 1 M was slowly added & the following plot was obtained. The percentage purity of H2SO4 sample and slope of the curve respectively are: 1 1 (A) 50%,  (B) 75%,  3 2 (C) 75% , –1 (D) none of these

Q.19

Equal volumes of 10% (v/V) of HCl is mixed with 10% (v/V) NaOH solution. If density of pure NaOH is 1.5 times that of pure HCl then the resultant solution be. (A) basic (B) neutral (C) acidic (D) can’t be predicted.

Q.20

The mole fraction of a given sample of I2 in C6H6 is 0.2. The molality of I2 in C6H6 is (A) 0.32 (B) 3.2 (C) 0.032 (D) 0.48

Q.21

A sample of H2SO4 (density 1.8 g/ml) is 90% by weight. What is the volume of the acid that has to be used to make 1 litre of 0.2 –M H2SO4 ? (A) 16 mL (B) 10 mL (C) 12 mL (D) 18 mL

Q.22

What volume of HNO3 (sp. gravity 1.05 g ml–1 containing 9%(w/w) of HNO3 reducing to NOg ) is required to oxidise iron 1 g FeSO4. 7H2O in acid medium is (A) 70 ml (B) 0.80 ml (C) 80 ml (D) 0.65 ml

Q.23

One litre of a sample of hard water contain 2.22 mg CaCl2 and 1.9 mg of MgCl2 in 1 L H2O. What is the total hardness in terms of ppm of CaCO3. [Ca = 40; Mg = 24, Cl = 35.5] (A) 2 ppm (B) 3 ppm (C) 4 ppm (D) 4.12 ppm


Q.24

10 L of hard water required 0.56 gm of lime for removing hardness. Hence temporary hardness in ppm of CaCO3 is (A) 100 (B) 200 (C) 10 (D) 20

Q.25

0.1 gm of a polyvalent metal of atomic mass 51.0 amu reacted with dilute sulphuric acid to give 43.9 ml of H2 at STP. The solution in the lower oxidation state was found to require 58.8 ml of N/10 KMnO4 solution for complete oxidation. The valencies of the metal is (A) M2+ and M5+ (B) M3+ and M6+ (C) M1+ and M5+ (D) M2+ and M3+

Q.26

Equivalent weight of H3PO2 when it disproportionate into PH3 and H3PO3 is (A) M (B) M/2 (C) M/4 (D) 3M/4

Q.27

A mixture of NaHC2O4 and KHC2O4 · H2C2O4 required equal volumes of 0.2 N KMnO4 and 0.12 N NaOH separately. What is the molar ratio of NaHC2O4 and KHC2O4 · H2C2O4 in the mixture? (A) 6 : 1 (B) 1 : 6 (C) 1 : 3 (D) none

Q.28

100 cm3 of a solution of an acid (Molar mass = 82) containing 39 gm of the acid per litre were completely neutralized by 95.0 cm3 of aq. NaOH containing 20 gm of NaOH per 500 cm3. The basicity of the acid is (A) 1 (B) 2 (C) 3 (D) data insufficient

Q.29

Which of the following is correct for 17 g/L of H2O2 solution. (I) Volume strength is 5.6 at 273 K and 1 atm (II) Molarity of solution is 0.5 M (III) 1 ml of this solution gives 2.8 ml O2 at 273 K and 2 atm (IV) The normality of solution is 2M (A) I, II, III (B) II, III (C) II, III, IV

(D) I, II, III, IV

Q.30

In iodometric estimation of Cu2+ ion, the following reaction took place. 2Cu2+ + 4I– — Cu2I2 + I2 I2 + 2Na2S2O3 — 2NaI + Na2S4O6 If 100 ml of CuSO4 solution added to excess KI requires 50 ml of 0.2 M Na2S2O3, the molarity of CuSO4 solution is (A) 0.05 M (B) 0.1 M (C) 0.2 (D) 0.25

Q.31

500 ml of a sample of H2O2 marked 33.6 volumes is used as source of oxygen. This sample partly reacted with certain reactive impurities causing wastage of half the amount of H2O2 present. Volume of O2 available at 570 mm Hg & 27°C is: (A) 12.3 L (B) 24.6 L (C) 16.8 L (D) none of these

Q.32

Calculate the mass of anhydrous oxalic acid, which can be oxidised to CO2(g) by 100 ml of an MnO 4 solution, 10 ml of which is capable of oxidising 50 ml of 1N I– to I2. (A) 45 gm

(B) 22.5 gm

(C) 30 gm

(D) 12.25 gm


Q.33

Three different solutions of oxidising agents KMnO4, K2Cr2O7 and I2 is titrated seperately with 0.158 gm of Na2S2O3. If molarity of each oxidising agent is 0.1 M and reactions are MnO 4 + S2 O 32  MnO2 + SO 24 Cr2 O 72 + S2 O 32  Cr3+ + SO 24 – I2 + Na2S2O3  Starch  Na2S4O6 + I

Then (A) volume of KMnO4 used is maximum (C) wt. of I2 used in titration is maximum

(B) volume of K2Cr2O7 used is minimum (D) none

Q.34

Find out % of oxalate ion in a given sample of an alkali metal oxalate salt, 0.30 gm of it is dissolved in 100 CC water required 90 CC of centimolar KMnO 4 solution in acidic medium. (A) 66% (B) 55% (C) 44% (D) 88%

Q.35

1 gram at a sample of CaCO3 was strongly heated and the CO2 liberated was absorbed in 100 mL of 0.5 M NaOH. Assuming 90% purity for the sample. How much mL of 0.5 M HCl would be required to react with the solution of the alkali to reach the phenolphthalein end point? (A) 73 mL (B) 41 mL (C) 82 mL (D) 87 mL

Q.36

A 0.518 g sample of lime stone is dissolved in HCl and then the calcium is precipitated as CaC2O4. After filtering and washing the precipitate, it requires 40.0 mL of 0.250 N KMnO4, solution acidified with H2SO4 to titrate it as, MnO 4 + H+ + C 2 O 24   Mn2+ + CO2 + 2H2O The percentage of CaO in the sample is: (A) 54.0% (B) 27.1% (C) 42%

(D) 84%

Q.37

0.3 g of an oxalate salt was dissolved in 100 mL solution. The solution required 90 mL of N/20 KMnO4 for complete oxidation. The % of oxalalte ion in salt is: (A) 33% (B) 66% (C) 70% (D) 40%

Q.38

A sample of H2O2 solution labelled as 33.6 volume has density of 264 gm/lit. Mark the correct option representing concentration of same solution in other units. [Solution contains only H2O & H2O2] (A) Mole fraction of H2O2 in the solution = 0.5 (B) % w/v = 102% (C) M H 2O 2 = 6 M 1000 m 54 Match the n-factor of following reactant : (i) As2S3  AsO43– + SO42– (half reaction) (a) 10 (ii) Bi2S3  Bi+5 + S (half reaction) (b) 4 2– – (iii) Mn(NO3)2  MnO4 + NO3 (half reaction) (c) 2/3 (iv) 5P2H4  6PH3 + P4H2 (d) 6/5 2– – – (v) MnO4 + H2O  MnO2 + MnO4 + OH (e) 28 (A) (i)-(a), (ii)-(b), (iii)-(c), (iv)-(d), (v)-(e) (B) (i)-(c), (ii)-(a), (iii)-(b), (iv)-(d), (v)-(e) (C) (i)-(e), (ii)-(a), (iii)-(b), (iv)-(d), (v)-(c) (D) (i)-(e), (ii)-(b), (iii)-(a), (iv)-(c), (v)-(d)

(D) m H 2O 2 = Q.39


Question No. 40 to 43 (4 questions) A 4.925 g sample of a mixture of CuCl2 and CuBr2 was dissolved in water and mixed thoroughly with a 5.74 g portion of AgCl. After the reaction the solid, a mixture of AgCl and AgBr, was filtered, washed, and dried. Its mass was found to be 6.63 g. Q.40 Q.41 Q.42 Q.43

% By mass of CuBr2 in original mixture is (A) 2.24 (B) 74.5

(C) 45.3

% By mass of Cu in original mixture is (A) 38.68 (B) 19.05 (C) 3.86 % by mole of AgBr in dried precipate is (A) 25 (B) 50 (C) 75 – No. of moles of Cl ion present in the solution after precipitation are (A) 0.06 (B) 0.02 (C) 0.04

(D) None (D) None (D) 60 (D) None

Question No. 44 to 46 (3 questions) NaBr, used to produce AgBr for use in photography can be self prepared as follows : Fe + Br2  FeBr2 ....(i) FeBr2 + Br2  Fe3Br8 ....(ii) (not balanced) Fe3Br8 + Na2CO3  NaBr + CO2 + Fe3O4 ....(iii) (not balanced) Q.44 Q.45

Q.46

Q.47 Q.48

Q.49 Q.50

Mass of iron required to produce 2.06 × 103 kg NaBr (A) 420 gm (B) 420 kg (C) 4.2 × 105 kg (D) 4.2 × 108 gm If the yield of (ii) is 60% & (iii) reaction is 70% then mass of iron required to produce 2.06 × 103 kg NaBr (A) 105 kg (B) 105 gm (C) 103 kg (D) None If yield of (iii) reaction is 90% then mole of CO2 formed when 2.06 × 103 gm NaBr is formed (A) 20 (B) 10 (C) 40 (D) None Question No. 47 and 48 are based on the following piece of information. Mark the appropriate options on the basis of information. 342 gm of 20% by mass of Ba(OH)2 solution (sp. gr. 0.57) is reacted with 200 ml of 2M HNO3 according to given balanced reaction. Ba(OH)2 + 2HNO3  Ba(NO3)2 + 2H2O The nature of the final solution is (A) acidic (B) neutral (C) basic (D) can't say If density of final solution is 1.01 gm /ml then find the molarity of the ion in resulting solution by which nature of the above solution is identified, is (A) 0.5 M (B) 0.8 M (C) 0.4 M (D) 1 M Question No. 49 to 50 (2 questions) In the gravimetric determination of sulfur the ignited precipitate of BaSO4 sometimes partially reduces to BaS. This cause an error, of course, if the analyst does not realize this and thinks entire precipitate as BaSO4. Suppose a sample which contains 32.3% SO3 is analyzed and 20.0% of the final precipitate that is weighed is BaS. (80.0% is BaSO4). Calculate the mass of sample, assuming 100 gm precipitate is formed (A) 106.3 gm (B) 114.35 gm (C) 110.5 gm (D) None Percentage of SO3 in the sample, calculated by analyst is (if the assume the entire 100 gm precipiate as BaSO4) (A) 30 (B) 30.5 (C) 32 (D) 32.3 Digital Chemistry labs Pvt Ltd 403 Maha Laxmi Plaza Jawahar Nagar Kota (Raj.) Pin :- 324005 Phone :- 9929617387 Fax :- 0744 - 2405300

EXERCISE-IV Q.1

The number of moles of KMnO4 that will be needed to react with one mole of sulphite ions in acidic solution is [JEE 1997 ] (A) 2/5 (B) 3/5 (C) 4/5 (D) 1

Q.2

The normality of 0.3 M phosphorus acid (H3PO3) is (A) 0.1 (B) 0.9 (C) 0.3

[JEE 1999 ] (D) 0.6

Q.3

One mole of calciums phosphide on reaction with excess of water gives [JEE 1999 ] (A) one mole of phosphine (B) Two moles of phsophoric acid (C) Two moles of phosphine (D) One mole of phosphorus pentoxide

Q.4

An aqueous solution of 6.3 gm of oxalic acid dihydrate is made upto 250 ml. The volume of 0.1 N NaOH required to completely neutralize 10 ml of this solution is [JEE 2001 ] (A) 40 ml (B) 20 ml (C) 10 ml (D) 4 ml

Q.5

In the standarization of Na2S2O3 using K2Cr2O7 by iodometry the equivalent mass of K2Cr2O7 is (A)

M. Mass 2

(B)

M. Mass 6

(C)

M. Mass 3

(D) Same as M. Mass. [JEE 2001 ]

Q.6

How many moles of electrons weigh one kilogram (A) 6.02 ×

Q.7

1023

1 (B) × 1031 9.108

Which has maximum number of atoms? (A) 24 g C (12) (B) 56 g Fe (56)

6.023 (C) × 1054 9.108

(C) 27g Al (27)

1 108  (D) 9.108 6.02 [JEE 2002 ]

[JEE 2003 ] (D) 108 g Ag (108)

SUBJECTIVES Q.8

One litre of a mixture of O2 and O3 at NTP was allowed to react with an excess of acidified solution of KI. The iodine liberated required 40 ml of M/10 sodium thiosulphate solution for titration. What is the percent of ozone in the mixture? Ultraviolet radiation of wavelength 300 nm can decompose ozone. Assuming that one photon can decompose one ozone molecule, how many photons would have been required for the complete decomposition of ozone in the original mixture? [ JEE’97, 5 ]

Q.9

A sample of hard water contains 96 ppm of SO 24  and 183 ppm of HCO3 , with Ca2+ as the only cation. How many moles of CaO will be required to remove HCO 3 from 1000 kg of this water? If 1000 kg of this water is treated with the amount of CaO calculate above, what will be the conentration (in ppm) of residual Ca2+ ions (Assume CaCO3 to be completely insoluble in water)? If the Ca2+ ions in one litre of the treated water are completely exchanged with hydrogen ions, what will be its pH (one ppm means one part of the substance in one million part of water, weight/ weights)? [JEE’ 1997]

Q.10

An aqueous solution containing 0.10g KIO3 (formula wt. = 214.0) was treated with an excess of KI solution. The solution was acidified with HCl. The liberated I2 consumed 45.0 ml of thiosulphate solution to decolourise the blue starch  iodine complex. Calculate the molarity of the sodium thiosulphate solution. [ JEE’ 1998] Digital Chemistry labs Pvt Ltd 403 Maha Laxmi Plaza Jawahar Nagar Kota (Raj.) Pin :- 324005 Phone :- 9929617387 Fax :- 0744 - 2405300

Q.11 Q.12

How many millilitre of 0.5 M H2SO4 are needed to dissolve 0.5 gm of copper II carbonate? [JEE’ 1999] A plant virus is found to consist of uniform cylindrical particles of 150Å in diameter and 5000Å long. The specific volume of the virus is 0.75 cm3/gm. If the virus is considered to be a single particle, find its molecular weight. [JEE’ 1999]

Q.13

Hydrogen peroxide solution (20 mL) reacts quantitatively with a solution of KMnO4 (20 mL) acidified with dilute H2SO4. The same volume of the KMnO4 solution is just decolorized by 10mL of MnSO4 in neutral medium simultaneously forming a dark brown precipitate of hydrated MnO2. The brown precipitate is dissolved in 10mL of 0.2M sodium oxalate under boiling condition in the presence of dilute H2SO4. Write the balanced equations involved in the reactions and calculate the molarity of H2O2. [JEE’ 2001]

Q.14

Calculate the molarity of water if its density is 1000 kg/m3.

Q.15

1 gm charcoal is placed in 100 ml of 0.5 M CH3COOH to form an adsorbed mono-layer of acetic acid molecule and thereby the molarity of CH3COOH reduces to 0.49. Calculate the surface area of charcoal adsorbed by each molecule of acetic acid. Surface area of charcoal = 3.01 × 102 m2/g. [JEE’ 2003]

Q.16

20% of surface sites are occupied by N2 molecules. Number of surface sites per unit area is 6.023 × 1014 cm–2 and total area of catalyst surface is 1000 cm2 . Now when catalyst is heated to300K N2 gas desorbed and evolved gas occupied, 2.46 cm3 at 0.001 atm. Find the no. of sitesocupied by each molecule of N2. [JEE 2005]


[JEE’ 2003]

ANSWER KEY

EXERCISE-I Q.1

1.33 × 1021

Q.2

2.4 L

Q.3

166.6 ml

Q.4

y atoms

Q.5

33.9

Q.6

4.44×10 22

Q.7

0.05, 0.027

Q.8

2.22g ; 0.948g

Q.9

0.532 : 1

Q.10

9.063 gm

Q.11

0.250

Q.12

1.14 g

Q.13

10 11 5 B =80%; 5 B =

Q.14

C5H14N 2

Q.15

C3H6O; C6H12O2

Q.19

At. wt. of Y = 70 amu

20%

Q.16 108 Ag, 1.41 gm

Q.17 41

Q.18 108.16

Q.20

29.29%

Q.21

35.77%

Q.22

(a) 26.25%, (b) 11.46%

Q.23

4.9 ml

Q.24

1.03 gm

Q.25

4.02%, 53.35%

Q.26

21.68%

Q.27

%NaHCO3 = 16.8, % Na2CO3= 83.2

Q.28

67.9%

Q.29

1.445 M

Q.30

1.088 M, 1.13 m

Q.31

13.15 M

Q.32

16.67%

Q.33

2.7 × 10–4 m

Q.35

1.71 M

Q.36 15.96 m

Q.39

(a) 1.2 M ; (b) 9.18 × 10–3; (c) 1.2 × 104 ppm

Q.40

V = 157.8 ml

Q.43

MgCO3 = 52.02%, CaCO3 = 47.98 %

Q.44

83.33

Q.41

20.72 %

Q.37 0.1N Q.42

Q.45 0.424 gm; 0.21gm

Q.34

1736.1 ml

Q.38 1 : 2

200 mL Q.46 23.2 gm, 22.28gm

Q.47 0.06gm; .0265gm

Q.48 4.24 g/L; 5.04 g/L

Q.50

zero

Q.51

V = 31.68 ml Q.52

Q.54

0.15 N

Q.55

H2C2O4. 2H2O = 14.35%, KHC2O4. H2O = 81.71%

Q.56 1.406%

Q.57 90.1%

Q.60

CO = 5 ml ; CH4 = 2 ml ; N2 = 3 ml

Q.62

C 2H 6 O

Q.64

H2 : 12.50%, CH4: 7.50%, N2 : 80%

Q.63

4 :1

337 mL

Q.58

0.1281 g

Q.61

10 ml

Q.65

C 2H 4

Q.49

+3

Q.53

41.53%

Q.59

0.174g; 3.48%

\

PROFICIENCY TEST Q.1 1.

6.02 × 1023

5.

Laws of conservation of mass

8.

3

9.

12.

44.8 L

16.

2.

2 × 10–3 mol

3.

36 ml

4.

4.48 L

6.

16 gm

7.

GAM

14.2 gm

10.

44 g mol–1

11.

4.13 g

13.

24.3

14.

A2B

15.

Conservation of mass

0.4

17.

0.1

18.

M/2

19.

0.1168

20.

12

21.

3.3125 g

22.

50

23.

5

24.

0.4 M

25.

S8

False

2.

False

3.

False

4.

True

Q.2 1.


5.

True

6.

True

7.

False

8.

False

9.

True

10.

True

11.

True

12.

False

13.

True

14.

True

15.

False

16.

False

17.

False

18.

True

19.

True

20.

False

21.

False

22.

True

23.

False

24.

False

25.

True Q.3

18.33

EXERCISE-II Q.1

76.15%

Q.2

Al = 0.566 g; Mg = 0.434 g

Q.4

1.09 × 10–3 gm

Q.5

(a)10 mol, (b) 25 lit., (c) 2.5

Q.6

NaHCO3= 42%, Na2CO3 = 26.5%, Na2SO4 = 31.5%

Q.7

(i) 28%, (ii) 33.33%, (iii) 0.8g

Q.8

0.5 : 0.1 : 0.4

Q.9

FeO = 13.34%; Fe2O3 = 86.66%

Q.10

34.4 ml; 55.8 ml; 21.3 ml

Q.11

15.4%

Q.12

XeF6

Q.13

30.55kg, 6 electrons

Q.14

5g

Q.15

VKIO3 = 0.42 mL, [HCl] = 0.02N

Q.16

57.4% CuS, 42.6% Cu2S

Q.17

4.67L

Q.19

Fe = 5.6%, Cu = 1.27%

Q.20

CuS = 57.9% Q.21

Q.22

n = 4, NaOH = 6.4 g

Q.23

10%

Q.24

RCu = 269

Q.25

Q.18

1.75% 95.15%

41.6%

EXERCISE-III Q.1 Q.8 Q.15 Q.22 Q.29 Q.36 Q.43 Q.50

C D A,D B A A A A

Q.2 Q.9 Q.16 Q.23 Q.30 Q.37 Q.44

D B B C B B B

Q.3 Q.10 Q.17 Q.24 Q.31 Q.38 Q.45

C A B A A D C

Q.4 Q.11 Q.18 Q.25 Q.32 Q.39 Q.46

C C C A B C B

Q.5 Q.12 Q.19 Q.26 Q.33 Q.40 Q.47

D C A D A C C

Q.6 Q.13 Q.20 Q.27 Q.34 Q.41 Q.48

C C B D A A A

Q.7 Q.14 Q.21 Q.28 Q.35 Q.42 Q.49

B A C B C D B

B

Q.6

D

Q.7

A

EXERCISE-IV Q.1

A

Q.2

D

Q.3

C

Q.4

A

Q.5

SUBJECTIVES Q.8

6.57% O3(by weight), 1.2 × 1021 photons

Q.9

1.5, 40 ppm, pH = 2.6989

Q.10

0.0623M

Q.11

8.097 ml

Q.12

7.095 × 107

Q.13

0.1M

Q.14

55.55

Q.15

5 × 10–19 m2

Q.16

2


STOICHIOMETRY

Recommend Documents