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Classified Chemistry IGCSE

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Topic 13

 Hydrogen  Nitrogen  Ammonia and fertilizers  Sulfur and sulfur dioxide  Making of sulfuric acid  Caron cycle  Green house and global worming  Carbonates

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Mostafa Barakat (0100 165 44 62)


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1) Nov 2001 Q (5_a) a) In the USA, sulfur is obtained from underground deposits. It burns to form sulfur dioxide. This is used in paper making, to preserve food and in the manufacture of sulfuric acid (i) Why is sulfur dioxide needed in paper making? to bleach it ………………………………………………………………………………………… ………………………………………………………………………………………[1] (ii) How does sulfur dioxide preserve food? kills bacteria ………………………………………………………………………………………… ………………………………………………………………………………………[1]

2) June 2002 Q (2_a) a) Fermentation of sugars is one method of making ethanol. Vines produce glucose by photosynthesis. The glucose collects in the grapes which grow in clusters on the vine.

a) Vines are attacked by a fungus that ruins the grapes. In 1882 it was discovered that spraying the vines with Bordeaux mixture killed the fungus The fungicide, Bordeaux mixture, contains water, calcium hydroxide and copper (II) sulphate. (i) Name the raw material from which calcium hydroxide is made. calcium oxide ………………………………………………………………………………………… ………………………………………………………………………………………[1]

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3) Nov 2002 Q (1_a) a) Sulfuric acid is made by the Contact Process.

2SO 2( g )  O 2( g )

2SO3( g )

the forward reaction is exothermic

(i) What are the reaction conditions for the Contact Process? 1) temperature = 300 C 2) pressure from 2 to 10 atmp ………………………………………………………………………………………… 3) catalyst vanadium(V) oxide ………………………………………………………………………………………[3] (ii) Would the yield of sulphur trioxide increase, decrease or stay the same when the temperature is increased? Explain your answer. ………………………………………………………………………………………… decrease because increase in temperature favours the backward reaction ………………………………………………………………………………………… ………………………………………………………………………………………[2] (iii) Describe how sulfur trioxide is changed into concentrated sulfuric acid. ………………………………………………………………………………………… dissolve sulfur trioxide in concentrated sulfuric acid then add water ………………………………………………………………………………………[2]

4) Nov 2003 Q (1_a, b) 1) Ammonia contains the elements nitrogen and hydrogen. It is manufactured from these elements in the Haber process.

N 2( g )

 3H 2( g )

2NH 3( g )

The forward reaction is exothermic. a) (i) Nitrogen is obtained from liquid air by fractional distillation. Why does this technique separate liquid oxygen and nitrogen? ………………………………………………………………………………………… because they differ in boiling point ………………………………………………………………………………………… Name two raw materials from which hydrogen is manufactured ………………………………………………………………………………………… methane and water ………………………………………………………………………………………[3] b) The table shows how the percentage of ammonia in the equilibrium mixture varies with pressure at 600 °C.

(i) Explain why the percentage of ammonia increases as the pressure increases because increase in pressure moves the reaction to the right because it is ………………………………………………………………………………………… side of lower moles ………………………………………………………………………………………[2] 13 – Non-metals



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(ii) How would the percentage of ammonia change if the measurements had been made at a lower temperature? Explain your answer the percentage of ammonia would increase because the forward reaction is exothermic. ………………………………………………………………………………………… An increase in temperature moves position of equilibrium to the right, that is ………………………………………………………………………………………… more ammonia ………………………………………………………………………………………[2] (iii) State two of the reaction conditions used in the Haber process. ………………………………………………………………………………………… 1) temperature = 300 to 600 C 2) catalyst = iron 3) pressure = 200 atmp ………………………………………………………………………………………[2]

5) Nov 2003 Q (5_a, b) 5) Sulphur dioxide, SO2, and sulphur trioxide, SO3, are the two oxides of sulphur. a) Sulphur dioxide can kill bacteria and has bleaching properties. Give a use of sulphur dioxide that depends on each of these properties

(i) ability to kill bacteria

preserve food …………………………………………………. [1]

making papers (ii) bleaching properties …………………………………………………. [1] b) Sulphur trioxide can be made from sulphur dioxide. (i) Why is this reaction important industrially? to make sulfuric acid ………………………………………………………………………………………… ………………………………………………………………………………………[2] (ii) Complete the word equation. oxygen   sulphur trioxide sulphur dioxide + ………….………………………

[1]

(iii) What are the conditions for this reaction? 1) vanadium(V) oxide as oxide 2) temperature = 450 C ………………………………………………………………………………………… 3) pressure = 2 atmp ………………………………………………………………………………………[2]

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6) June 2004 Q (2_a, b) a) Sulphur is used to make sulfuric acid. In the UK, the annual production of the acid is about 2.5 million tonnes

(i) Give a large scale source of the element sulphur ………………………………………………………………………………………… USA or Texas or Poland or Mexico ………………………………………………………………………………………[1] (ii) State another use of sulphur dioxide. ………………………………………………………………………………………… Preserving food or bleaching wood ………………………………………………………………………………………[1] (iii) How is sulphur changed into sulphur dioxide? ………………………………………………………………………………………… burnt in oxygen or air ………………………………………………………………………………………[1] (iv) Name the catalyst used in reaction 2 ………………………………………………………………………………………… vanadium(V) oxide ………………………………………………………………………………………[1] (v) Reaction 2 is exothermic. Why is a catalyst, rather than a higher temperature, used to increase the rate of this reversible reaction? because Increase temperature increases rate but reduces yield catalyst only ………………………………………………………………………………………… increases rate or a catalyst does not influence position of equilibrium ………………………………………………………………………………………[2] (vi) Write a word equation for reaction 3. ………………………………………………………………………………………… sulphur trioxide + sulphuric acid oleum ………………………………………………………………………………………[1] (vii) Write a symbol equation for reaction 4. ………………………………………………………………………………………… H2S2O7 + H2O 2H2SO4 ………………………………………………………………………………………[1]

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b) About one third of this production of acid is used to make nitrogen and phosphorus containing fertilizers. (i) Name the third element that is essential for plant growth and is present in most fertilisers. potassium ………………………………………………………………………………………… ………………………………………………………………………………………[1] (ii) Name a nitrogen-containing fertilizer that is manufactured from sulphuric acid. ammonium sulphate ………………………………………………………………………………………… ………………………………………………………………………………………[1]

7) June 2005 Q (4_c) c) Sulfuric acid is manufactured by the Contact Process. Sulphur dioxide is oxidized to sulphur trioxide by oxygen.

2SO 2

 O2

  2SO3

(i) Name the catalyst used in this reaction ………………………………………………………………………………………… vanadium(V) oxide ………………………………………………………………………………………[1] (ii) What temperature is used for this reaction? ………………………………………………………………………………………… 450 C ………………………………………………………………………………………[1] (iii) Describe how sulphur trioxide is changed into sulfuric acid. ………………………………………………………………………………………… add to sulfur trioxide to concentrated sulphuric acid then add water ………………………………………………………………………………………[2]

8) Nov 2005 Q (7_a, b) In 1909, Haber discovered that nitrogen and hydrogen would react to form ammonia. The yield of ammonia was 8%.

a) Describe how hydrogen is obtained for the modern process. ………………………………………………………………………………………… from methane and water ………………………………………………………………………………………[2] b) (i) What is the catalyst in the modern process? ………………………………………………………………………………………… iron ………………………………………………………………………………………[1] 13 – Non-metals



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(ii) Explain why the modern process, which uses a lower temperature, has a higher yield of 15%. lower temperature moves equilibrium to right because forward reaction ………………………………………………………………………………………… is exothermic ………………………………………………………………………………………[2]

9) June 2006 Q (5_a) a) Sulfuric acid is made by the Contact process in the following sequence of reactions

(i) How is sulphur dioxide made from sulphur? ………………………………………………………………………………………… by Burn sulphur in air ………………………………………………………………………………………[1] (ii) Sulphur dioxide has other uses. Why is it used in the manufacture of paper? ………………………………………………………………………………………… to bleach it ………………………………………………………………………………………[1] (iii) How does it preserve food? ………………………………………………………………………………………… it kill bacteria ………………………………………………………………………………………[1] b) The equation for a stage of the Contact process is

2SO 2

 O2

2SO3

The percentage of sulphur trioxide in the equilibrium mixture varies with temperature

(i) How does the percentage of sulphur trioxide in the equilibrium mixture vary as the temperature increases? Circle the correct answer. Increase

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Stay the same

Decrease

[1]



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(ii) Is the forward reaction in the equilibrium 2SO2 + O2 2SO3 exothermic or endothermic? Give a reason for your choice. exothermic because increase temperature favours back reaction so it is ………………………………………………………………………………………… endothermic, so forward reaction must be exothermic ………………………………………………………………………………………[2] (iii) Explain, mentioning both rate and percentage yield, why the temperature used in the Contact process is 450 °C. Low enough for good yield ………………………………………………………………………………………… High enough for (economic) rate ………………………………………………………………………………………[2] (iv) Describe how the sulphur trioxide is changed into concentrated sulfuric acid. bubble sulfur trioxide into concentrated sulfuric acid then add water ………………………………………………………………………………………… ………………………………………………………………………………………[2]

10) Nov 2006 Q (5_a, b) Ammonia is manufactured by the Haber process.

The forward reaction is exothermic a) (i) What is the catalyst for this reaction? iron ………………………………………………………………………………………… ………………………………………………………………………………………[1] (ii) Newer catalysts have been discovered for this process. Using these catalysts, the operating temperature is lowered from 450 C to 400 C. What is the advantage of using a lower temperature? Explain your answer Advantage

higher yield ……………………………………………………………………….

Explanation

lower temperature favours the exothermic reaction that is the ……………………………………………………………………..... forward reaction ……………………………………………………………………[2]

b) After passing over the catalyst, the mixture contains 15% of ammonia. It is cooled and the ammonia liquefies and is separated from the unreacted nitrogen and hydrogen. They are recycled. (i) How are the gases recycled? Sent over the catalyst again to make more ammonia ………………………………………………………………………………………… ………………………………………………………………………………………[1]

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(ii) Only ammonia gas liquefies. Suggest an explanation for this. because It has the highest boiling point ………………………………………………………………………………………… ………………………………………………………………………………………[1]

11) Nov 2007 Q (4_a) a) Zinc blende is heated in air to give zinc oxide and sulphur dioxide. Most of the sulphur dioxide is used to make sulphur trioxide. This is used to manufacture sulphuric acid. Some of the acid is used in the plant, but most of it is used to make fertilisers. (i) Give another use of sulphur dioxide. bleach wood ………………………………………………………………………………………… ………………………………………………………………………………………[1] (ii) Describe how sulphur dioxide is converted into sulphur trioxide react with oxygen at 450°C and in the presence of vanadium(V) oxide as catalyst ………………………………………………………………………………………… and 2 atmospheric pressure ………………………………………………………………………………………… ………………………………………………………………………………………[3] (iii) Name a fertiliser made from sulphuric acid. ………………………………………………………………………………………… ammonium sulfate ………………………………………………………………………………………[1]

12) June 2009 Q (6_a) 6 Ammonia is manufactured by the Haber process N2(g) + 3H2(g)

2NH3(g) the forward reaction is exothermic

a) (i) Name the raw materials from which nitrogen and hydrogen are obtained Nitrogen from

air …………….……………………………………………………[1]

Hydrogen from

water …………….……………………………………………………[1]

(ii) Name the catalyst used in this process. ………………………………………………………………………………………… iron ………………………………………………………………………………………[1] (iii) What is the most important use of ammonia? ………………………………………………………………………………………… making fertilizers ………………………………………………………………………………………[1]

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13) Nov 2009 Q (6_a) a) Sulfuric acid is made by the contact process

2SO 2

 O2

2SO3

This is carried out in the presence of a catalyst at 450 C and 2 atmospheric pressure (i) How is the sulfur dioxide made? by burn sulfur in air ………………………………………………………………………………………… ………………………………………………………………………………………[1] (ii) give another use of sulfur dioxide bleach for wood pulp ………………………………………………………………………………………… ………………………………………………………………………………………[1] (iii) name the catalyst used vanadium(V) oxide ………………………………………………………………………………………… ………………………………………………………………………………………[1] (iv) if the temperature is decreased to 300° C, the yield of sulfur trioxide increases. Explain why this lower temperature is not used ………………………………………………………………………………………… because rate too slow and not economic ………………………………………………………………………………………[1] (v) sulfur trioxide is dissolved in concentrated sulfuric acid. This added to water make more sulfuric acid. Why is sulfur trioxide not added directly to water? because reaction too violent ………………………………………………………………………………………… ………………………………………………………………………………………[1] 14) June 2010 [31] Q (1_iv) 1 Choose an element which fits each of the following descriptions. (iv) It has a basic oxide of the type MO which is used to treat acidic soils. calcium .................................................................................................................................. [1]

15) June 2010 [31] Q (8_b, i) (b) In some areas when water is boiled, the inside of kettles becomes coated with a layer of calcium carbonate. This can be removed by adding methanoic acid. (i) Complete the equation.

.......2 HCOOH  CaCO3

CO2  ........... H2O   Ca(HCOO )2  .......... [2]

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16) Nov 2010 [31] Q (7) 7 The diagram shows part of the carbon cycle. This includes some of the processes which determine the percentage of carbon dioxide in the atmosphere.

(i) Carbon dioxide is one greenhouse gas. Name another one. methane ....................................................................................................................... [1] (ii) Explain the term respiration and how this process increases the percentage of carbon dioxide in the atmosphere. living organisms produce energy from food ............................................................................................................................ this forms carbon dioxide which leads to increase the percentage of carbon ............................................................................................................................ dioxide in air ....................................................................................................................... [3] (iii) Explain why the combustion of waste crop material should not alter the percentage of carbon dioxide in the atmosphere. when growing the crop removed carbon dioxide from atmosphere ............................................................................................................................ while combustion returned the carbon dioxide ....................................................................................................................... [2] (iv) In 1960 the percentage of carbon dioxide in the atmosphere was 0.032% and in 2008 it was 0.038%. Suggest an explanation for this increase. due to the increased combustion of fossil fuels ............................................................................................................................ ....................................................................................................................... [2]

17) Nov 2010 [32] Q (7_a, b) 7 The major use of sulfur dioxide is to manufacture sulfuric acid. (a) (i) Another use of sulfur dioxide is as the food additive E220. How does it preserve food? it kill bacteria ............................................................................................................................ ....................................................................................................................... [1] (ii) Why is sulfur dioxide used in the manufacture of wood pulp? to bleach it ....................................................................................................................... [1]

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(iii) How is sulfur dioxide manufactured? by burn sulfur in air ....................................................................................................................... [1] (b) Complete the following description of the manufacture of sulfuric acid. oxygen Sulfur dioxide reacts with .................................. to form sulfur trioxide. vanadium(V) oxide The above reaction is catalysed by ................................................. . 450 The optimum temperature for this reaction is .............................. °C. water Sulfur trioxide needs to react with ............................... to form sulfuric acid. [4]

18) Nov 2011 [32] Q (2) 2 Sulfur is needed for the production of sulfuric acid. Two of the major sources of sulfur are ● underground deposits of the element sulfur, ● sulfur compounds from natural gas and petroleum. (a) Explain why sulfur and its compounds are removed from these fuels before they are burned. because it burns to form sulfur dioxide which dissolve in water vapour ....................................................................................................................................... which causes acid rain .................................................................................................................................. [2] (b) Sulfur dioxide is made by spraying molten sulfur into air. The sulfur ignites and sulfur dioxide is formed. (i) Suggest why molten sulfur is used in the form of a fine spray. because it has bigger surface area which reacts faster ....................................................................................................................................... .................................................................................................................................. [2]

(ii) Explain why traces of sulfur dioxide act as a preservative in fruit juices. because it kills microbes .................................................................................................................................. [1] (iii) State another use of sulfur dioxide. bleach wood .................................................................................................................................. [1] (c) Describe how sulfur dioxide is changed into sulfur trioxide. Give the reaction conditions and an equation. heat sulfur dioxide in air 2 SO2 + O2 SO 3 ....................................................................................................................................... conditions 1) temperature = 450 C ....................................................................................................................................... 2) catalyst = vanadium(V) oxide ....................................................................................................................................... 3) pressure = 2 atmp .................................................................................................................................. [4] (d) Complete the following equations for the formation of sulfuric acid from sulfur trioxide. H2 SO4 SO3  ...............   H 2S 2O7 H2 O  2 H 2SO 4 H 2S 2O7  ............  ..........

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19) Nov 2011 [3 3] Q (3) 3 Fertilisers are used to promote plant growth. Two fertilisers are ammonium phosphate, (NH4)3PO4, and calcium dihydrogen phosphate, Ca(H2PO4)2. (a) Describe a test to distinguish between these two fertilisers. add sodium hydroxide solution then warm test ................................................................................................................................. .................................................................................................................................. [2]

only ammonium phosphate gives off ammonia gas which will turn red result .............................................................................................................................. litmus paper blue .................................................................................................................................. [1] (b) Many fertilisers are manufactured from ammonia. Describe how ammonia is made in the Haber process. Give the essential conditions and an equation for the process. by direct combination between nitrogen and hydrogen (N2 + 3 H2 NH3) ....................................................................................................................................... 1) temperature = 450 C ....................................................................................................................................... 2) pressure = 200 atmospheres ....................................................................................................................................... 3) catalyst = iron .................................................................................................................................. [4] (c) State the essential plant nutrient not supplied by ammonium phosphate. potassium ....................................................................................................................... [1] (d) The soluble compound, calcium dihydrogenphosphate is made by heating the insoluble mineral rock phosphate, Ca3(PO4)2, with sulfuric acid. (i) Why would rock phosphate not be effective as a fertiliser? because it needs to be soluble .............................................................................................................................. [1]

20) Nov 2011 [32] Q (3) 3 Fertilisers are used to promote plant growth. Two fertilisers are ammonium phosphate, (NH4)3PO4, and calcium dihydrogen phosphate, Ca(H2PO4)2. (a) Describe a test to distinguish between these two fertilisers. test ................................................................................................................................. .................................................................................................................................. [2] result .............................................................................................................................. .................................................................................................................................. [1]

(b) Many fertilisers are manufactured from ammonia. Describe how ammonia is made in the Haber process. Give the essential conditions and an equation for the process. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... .................................................................................................................................. [4]

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(c) State the essential plant nutrient not supplied by ammonium phosphate. ....................................................................................................................... [1] (d) The soluble compound, calcium dihydrogenphosphate is made by heating the insoluble mineral rock phosphate, Ca3(PO4)2, with sulfuric acid. (i) Why would rock phosphate not be effective as a fertiliser? .............................................................................................................................. [1]

21) Nov 2012 [32] Q (5) 5 The food additive E220 is sulfur dioxide. It is a preservative for a variety of foods and drinks. (a) State two other uses of sulfur dioxide. bleaching wood pulp ............................................................................................................................ manufacture of sulfuric acid ....................................................................................................................... [2] (b) How is sulfur dioxide manufactured? by heating sulfur in air ............................................................................................................................ ....................................................................................................................... [2] (c) Sulfur dioxide is a reductant (reducing agent). Describe what you would see when aqueous sulfur dioxide is added to acidified potassium manganate(VII). the colour changed from purple to colourless ............................................................................................................................ ....................................................................................................................... [2]

22) Nov 2012 [33] Q (7_a, b) 7 Ammonia is made by the Haber process.

N 2( g )  3H 2( g )

2NH 3( g )

(a) State one major use of ammonia. making fertilizers ....................................................................................................................... [1] (b) Describe how hydrogen is obtained for the Haber process. by electrolysis of acidified water. Hydrogen gas formed at cathode ............................................................................................................................ ............................................................................................................................ ....................................................................................................................... [3] (c) This reaction is carried out at a high pressure, 200 atmospheres. State, with an explanation for each, two advantages of using a high pressure. 1) increase pressure increase the rate of the reaction ............................................................................................................................ 2) more collisions so the collisions are more frequent ............................................................................................................................ 3) higher yield because high pressure favours the reaction with less moles ............................................................................................................................ 4) high pressure means lower temperature can be used to achieve comparable rate ....................................................................................................................... [5] (thus saving energy); 13 – Non-metals



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23) June 2013 [32] Q (6_b) (b) Ammonia is manufactured by the Haber process. The economics of this process require that as much ammonia as possible is made as quickly as possible. Explain how this can be done using the following information. The conditions for the following reversible reaction are: ● 450 °C ● 200 atmospheres pressure ● iron catalyst

N 2( g )  3H 2( g )

2NH 3( g )

the reaction is exothermic

1) high pressure favours lower volume side ............................................................................................................................ 2) high pressure increases rate ............................................................................................................................ 3) catalyst increases rate or lowers activation energy ............................................................................................................................ 4) low temperature favours exothermic reaction which increases yield ............................................................................................................................ 5) low temperature gives low rate ............................................................................................................................ ....................................................................................................................... [5] 24) June 2013 [32] Q (3) 3 The diagram shows some of the processes which determine the percentage of carbon dioxide in the atmosphere.

(a) Explain how the following two processes alter the percentage of carbon dioxide in the atmosphere. (i) combustion complete combustion of fuels containing carbon produce carbon dioxide ............................................................................................................................ which increase percentage of CO2 in atmosphere ............................................................................................................................ ....................................................................................................................... [3] (ii) respiration living things (cells / plants / animals / humans) oxidise carbohydrate ............................................................................................................................ produces carbon dioxide ............................................................................................................................ ....................................................................................................................... [3] 13 – Non-metals



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(b) Photosynthesis reduces the percentage of carbon dioxide in the atmosphere. (i) Complete the word equation for photosynthesis. oxygen glucose carbon dioxide + water  + ........................  ........................ [2] (ii) State two essential conditions for the above reaction to occur. 1) light ............................................................................................................................ 2) chlorophyll ....................................................................................................................... [2]

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