C3 YIELD AND ATOM ECONOMYOF CHEMICAL REACTIONSQuestion Practice
Name: ________________________
Class: ________________________
Date: ________________________
Time: 95 minutes
Marks: 94 marks
Comments: GCSE CHEMISTRY ONLY
Page 1 of 37Immanuel+College
Magnesium reacts with steam to produce hydrogen gas and magnesium oxide.
A teacher demonstrated the reaction to a class. The figure below shows the apparatus theteacher used.
(a) (i) The hydrogen produced was collected.
Describe how to test the gas to show that it is hydrogen.
Test __________________________________________________________
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Result ________________________________________________________
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(2)
1
(ii) Explain why the magnesium has to be heated to start the reaction.
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(2)
Page 2 of 37Immanuel+College
(b) The equation for the reaction is:
Mg(s) + H2O(g) MgO(s) + H2(g)
(i) The teacher used 1.00 g of magnesium.
Use the equation to calculate the maximum mass of magnesium oxide produced.
Give your answer to three significant figures.
Relative atomic masses (A r): O = 16; Mg = 24
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Maximum mass = ____________________ g
(3)
(ii) The teacher’s demonstration produced 1.50 g of magnesium oxide.
Use your answer from part (b)(i) to calculate the percentage yield.
If you could not answer part (b)(i), use 1.82 g as the maximum mass of magnesiumoxide. This is not the answer to part (b)(i).
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Percentage yield = ____________________ %
(2)
(iii) Give one reason why the percentage yield is less than 100%.
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(1)
(Total 10 marks)
Page 3 of 37Immanuel+College
This question is about zinc and magnesium.
Zinc is produced by electrolysis of molten zinc chloride, as shown in the figure below.
(a) (i) Why must the zinc chloride be molten for electrolysis?
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(1)
2
(ii) Describe what happens at the negative electrode.
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(3)
(iii) Complete the half equation for the reaction at the positive electrode.
________ Cl2 + ________ e–
(1)
(b) Magnesium can be produced from magnesium oxide.
The equation for the reaction is:
Si(s) + 2 MgO(s) SiO2(s) + 2 Mg(g)
(i) How can you tell from the equation that the reaction is done at a high temperature?
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(1)
Page 4 of 37Immanuel+College
(ii) This reaction to produce magnesium from magnesium oxide is endothermic.
What is meant by an endothermic reaction?
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(1)
(iii) A company made magnesium using this reaction.
Calculate the mass of magnesium oxide needed to produce 1.2 tonnes ofmagnesium.
Relative atomic masses (Ar): O = 16; Mg = 24
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Mass of magnesium oxide needed = ____________________ tonnes
(3)
(iv) The company calculated that they would produce 1.2 tonnes of magnesium, but only0.9 tonnes was produced.
Calculate the percentage yield.
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Percentage yield = __________ %
(1)
(v) Give one reason why the calculated yield of magnesium might not be obtained.
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(1)
(Total 12 marks)
Page 5 of 37Immanuel+College
The symbol equation for the decomposition of hydrogen peroxide is:
2H2O2 → 2H2O + O2
(a) This reaction is exothermic.
What is an exothermic reaction?
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(1)
3
(b) A student measured the volume of oxygen produced by 50 cm3 of hydrogen peroxide.
Page 6 of 37Immanuel+College
The graph shows the results.
(i) Use the graph to describe the changes in the rate of the reaction from 0 to 35seconds.
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(3)
(ii) What was the total volume of oxygen gas collected?
________________________ cm3
(1)
(iii) The student had calculated that the hydrogen peroxide used shouldproduce 25 cm3 of oxygen.
Calculate the percentage yield of oxygen.
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Answer = ________________ %
(2)
Page 7 of 37Immanuel+College
(c) An increase in the temperature of the hydrogen peroxide increases the rate of the reaction.
Use your knowledge of particles to explain why.
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(3)
(Total 10 marks)
A student investigated the reactions of copper carbonate and copper oxide with dilutehydrochloric acid.
In both reactions one of the products is copper chloride.
(a) Describe how a sample of copper chloride crystals could be made from copper carbonateand dilute hydrochloric acid.
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(4)
4
Page 8 of 37Immanuel+College
(b) A student wanted to make 11.0 g of copper chloride.
The equation for the reaction is:
CuCO3 + 2HCl → CuCl2 + H2O + CO2
Relative atomic masses, Ar: H = 1; C = 12; O = 16; Cl = 35.5; Cu = 63.5
Calculate the mass of copper carbonate the student should react with dilute hydrochloricacid to make 11.0 g of copper chloride.
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Mass of copper carbonate = _________________________ g
(4)
(c) The percentage yield of copper chloride was 79.1 %.
Calculate the mass of copper chloride the student actually produced.
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Actual mass of copper chloride produced = ____________ g
(2)
Page 9 of 37Immanuel+College
(d) Look at the equations for the two reactions:
Reaction 1 CuCO3(s) + 2HCl(aq) → CuCl2(aq) + H2O(l) + CO2(g)
Reaction 2 CuO(s) + 2HCl(aq) → CuCl2(aq) + H2O(l)
Reactive formula masses: CuO = 79.5; HCl = 36.5; CuCl2 = 134.5; H2O = 18
The percentage atom economy for a reaction is calculated using:
Calculate the percentage atom economy for Reaction 2.
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Percentage atom economy = ________________________ %
(3)
(e) The atom economy for Reaction 1 is 68.45 %.Compare the atom economies of the two reactions for making copper chloride.
Give a reason for the difference.
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(1)
(Total 14 marks)
Page 10 of 37Immanuel+College
The graph in Figure 1 shows a flow diagram for the Haber process.
Figure 1
(a) (i) Hydrogen gas is obtained from methane.Name one source of methane.
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(1)
5
(ii) Air is the source used to produce nitrogen for the Haber process.Suggest why air must not get into the reactor.
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(2)
(iii) Describe what happens to the mixture of gases from the reactor.
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(3)
Page 11 of 37Immanuel+College
(b) The graph in Figure 2 shows the percentage yield of ammonia using different conditions.
Figure 2
(i) Use Figure 2 to suggest the conditions that produce the greatest yield of ammonia.
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(1)
Page 12 of 37Immanuel+College
(ii) Use Figure 2 to suggest and explain why the conditions used to produce ammonia inthe Haber process are a temperature of 450 °C and a pressure of 200 atmospheres.
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(5)
(Total 12 marks)
Page 13 of 37Immanuel+College
Ammonium sulfate and urea are made from ammonia. These compounds are used by farmers.
The flow diagram shows the stages to make ammonium sulfate and urea.
(a) Give two examples from the flow diagram of the efficient use of energy and raw materials.
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(2)
6
Page 14 of 37Immanuel+College
(b) The equation for the reaction in Stage 4 is shown below.
N2(g) + 3H2(g) 2NH3(g)
The forward reaction is exothermic.
State and explain:
(i) how a decrease in temperature would affect the yield of ammonia at equilibrium
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(2)
(ii) how an increase in pressure would affect the yield of ammonia at equilibrium.
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(2)
Page 15 of 37Immanuel+College
(c) The equation for the reaction in Stage 7 is shown below.
2 NH3ammonia
+ CO2NH2CONH2
urea+ H2O
The table gives the relative formula masses (Mr) of the reactants and the products for thisreaction.
Formula of reactant or product Relative formula masses (Mr)
NH3 17
CO2 44
NH2CONH2 60
H2O 18
Percentage atom economy can be calculated using:
Calculate the percentage atom economy for the reaction in Stage 7.
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Percentage atom economy = ____________________________ %
(2)
(Total 8 marks)
Percentage atom economy =
Page 16 of 37Immanuel+College
Aspirin tablets have important medical uses.
7
A student carried out an experiment to make aspirin. The method is given below.
1. Weigh 2.00 g of salicylic acid.2. Add 4 cm3 of ethanoic anhydride (an excess).3. Add 5 drops of concentrated sulfuric acid.4. Warm the mixture for 15 minutes.5. Add ice cold water to remove the excess ethanoic anhydride.6. Cool the mixture until a precipitate of aspirin is formed.7. Collect the precipitate and wash it with cold water.8. The precipitate of aspirin is dried and weighed.
(a) The equation for this reaction is shown below.
C7H6O3 + C4H6O3 → C9H8O4 + CH3COOH salicylic acid aspirin
Calculate the maximum mass of aspirin that could be made from 2.00 g of salicylic acid.
The relative formula mass (Mr) of salicylic acid, C7H6O3, is 138
The relative formula mass (Mr) of aspirin, C9H8O4, is 180
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Maximum mass of aspirin = _______________ g
(2)
Page 17 of 37Immanuel+College
(b) The student made 1.10 g of aspirin from 2.00 g of salicylic acid.
Calculate the percentage yield of aspirin for this experiment.
(If you did not answer part (a), assume that the maximum mass of aspirin that can bemade from 2.00 g of salicylic acid is 2.50 g. This is not the correct answer to part (a).)
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Percentage yield of aspirin = _______________ %
(2)
(c) Suggest one possible reason why this method does not give the maximum amount ofaspirin.
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(1)
(d) Concentrated sulfuric acid is a catalyst in this reaction.
Suggest how the use of a catalyst might reduce costs in the industrial production of aspirin.
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(1)
(Total 6 marks)
Page 18 of 37Immanuel+College
The Haber process is named after the German chemist, Fritz Haber.
The diagram shows the main stages in the Haber process.
Reproduced with the permission of Nelson Thornes Ltd from PATRICK FULLICK et al,
ISBN 0-7487-9644- 4. First published in 2006
An exothermic reaction takes place when nitrogen reacts with hydrogen to make ammonia.
The reaction can be represented by this equation.
N2 (g) + 3H2 (g) 3
8
2NH (g)
(a) Calculate the maximum mass of ammonia that could be made from 1000 g of nitrogen.
Relative atomic masses: H = 1; N = 14
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Mass _______________g
(3)
Page 19 of 37Immanuel+College
(b) At a temperature of 450 °C and 200 atmospheres the actual mass of ammonia producedwhen 1000 g of nitrogen is passed through the reactor is 304 g.
Calculate the percentage yield of ammonia produced in the reactor.
(If you did not answer part (a), then assume that the maximum mass of ammonia that canbe made from 1000 g of nitrogen is 1100 g. This is not the correct answer to part (a).)
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Percentage yield of ammonia = _______________ %
(2)
(c) State and explain:
(i) how a decrease in temperature would affect the yield of ammonia
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(2)
(ii) how an increase in pressure would affect the yield of ammonia.
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(2)
Page 20 of 37Immanuel+College
(d) Factories that make ammonia are often near to large towns.
Discuss the economic, safety and environmental factors to be considered when there is anammonia factory near a town.
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(3)
(Total 12 marks)
(a) Ammonia is manufactured from nitrogen and hydrogen. The equation for the reactionbetween them is:
N2(g) + 3H2(g) 3(g)
9
2NH
(i) What is the source of the nitrogen?
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(1)
(ii) Why does increasing the pressure increase the chance of molecules of hydrogenreacting with molecules of nitrogen?
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(1)
(iii) The percentage yield of ammonia is the percentage, by mass, of the nitrogen andhydrogen which has been converted to ammonia. Calculate the mass, in tonnes, ofammonia which can be produced from 90 tonnes of hydrogen when the percentageyield is 50%. The relative atomic masses are: H 1; N 14.
Show clearly how you get to your answer.
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Mass = ________________________ tonnes
(2)
Page 21 of 37Immanuel+College
(b) The percentage yield of ammonia depends on the temperature and pressure inside thereaction vessel. The set of graphs show this.
(i) MPa is the symbol for which unit?
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(1)
(ii) What is the percentage yield of ammonia produced at a temperature of 450 °C and apressure of 20 MPa?
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(1)
(iii) Suggest what changes the chemical engineers should make to both the temperatureand the pressure to increase the percentage yield of ammonia.
Temperature ___________________________________________________
Pressure ______________________________________________________
(1)
Page 22 of 37Immanuel+College
(iv) How can the rate of ammonia production be increased without changing thetemperature or pressure or the mass of hydrogen and nitrogen?
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(1)
(c) About four-fifths of ammonia production is used to produce fertilisers. One of them is knownas NPK. It is made in the following way.
• Some ammonia is converted to nitric acid which is then mixed with phosphoric acid.• The mixture is neutralised with more ammonia and the solution is partly evaporated.• Potassium chloride is added to form granules.• The granules are coated to make the fertiliser free-flowing.
Complete the flow-chart for the production of NPK by writing in the names of the correctchemicals in the six boxes.
(2)
(Total 10 marks)
Page 23 of 37Immanuel+College
Mark schemes
(a) (i) lit splint or ignite the gas11
(squeaky) pop / explosion1
(ii) because it provides energy (for the reaction)1
to break bonds (in the reactants) or so the particles collide successfully
ignore reference to frequency or rate of collisions
because it provides the activation energy gains 2 marks1
(b) (i) 1.67(g)
allow 1.66-1.68
correct answer (to 3 significant figures) with or without workinggains 3 marks
if answer incorrect allow up to 2 marks for the following steps:
24 → 401.00 → 40 / 24or
moles magnesium = 1 / 24 or 0.04(17)
multiply by 40
allow ecf from incorrect ratio or incorrect number of moles3
(ii) if correct answer from part (b)(i) used
allow ecf from part (b)(i)
89.8 or 90
if 1.82 g used
82.4 or 82
correct answer with or without working gains 2 marks
if answer incorrect, allow the following for 1 mark:
1.50 / 1.67 (or their answer from part (b)(i))
if 1.82 g used: 1.50 / 1.822
Page 24 of 37Immanuel+College
(iii) any one from:
ignore measurement errors
• not all the magnesium reacted
allow the reaction may be reversible• some of the magnesium oxide / product may have been left in the tube or
may have been lost
ignore magnesium lost• different / unexpected reaction• magnesium not pure
1
[10]
Page 25 of 37Immanuel+College
(a) (i) so ions can move (and carry charge)
accept so current can flow
allow so it can conduct (electricity)
allow so charged particles can move
do not accept so electrons can move1
(ii) because zinc ions gain electrons
accept because zinc ions are reduced1
2 (electrons)1
zinc is formed
accept correct half equation for 3 marks
if no mark gained allow
positive ions go to negative electrode or
opposites attract or
reduction (of zinc) or
(zinc) gains electrons for 1 mark1
(iii) 2 Cl– Cl2 + 2 e–
must be completely correct1
(b) (i) because the magnesium is a gas
allow magnesium goes from solid to gas1
(ii) (a reaction which) takes in energy (from the surroundings)
accept more energy needed to break bonds than released byforming bonds
accept correct reference to energy level diagram
allow (a reaction which) takes in heat (from the surroundings)1
(iii) (Mr MgO =) 40
accept (2 Mr MgO =) 801
1.2 / 24 (x40) or 0.05 (x40)
or
40 / 24 (x1.2) or 1.67 (x1.2)
allow ecf from step 11
2(.0)
2
Page 26 of 37Immanuel+College
allow ecf carried through from step 1
correct answer with or without working gains 3 marks1
(iv) 75(%)1
(v) any one from:• the reaction is reversible
accept incomplete reaction
ignore equilibrium not reached• some lost / escaped / released (when separated)• some of the reactant may react in different ways from the expected
reaction• impure reactant(s)
ignore measurement and calculation errors1
[12]
(a) gives out energy or heat13
(b) (i) accept qualified answers in terms of volume of gas related to time
fast initially1
slows down1
reaction stops
accept reaction is now very slow1
(b) (ii) 211
(iii) 84
correct answer with or without working = 2 marks
allow ecf from (b)(ii) correctly calculated for 2 marks
allow evidence of 21/25 or (b)(ii)/25 for 1 mark2
(c) because they / particles have more energy / move faster
ignore particles move more / vibrate1
(and so) particles collide more often / more frequently or particles more likely to collide
ignore collide faster
ignore more collisions1
Page 27 of 37Immanuel+College
(and) more of the collisions are successful or particles collide with more energy / harder ormore of the particles have the activation energy
accept more successful collisions1
[10]
(a) add excess copper carbonate (to dilute hydrochloric acid)
accept alternatives to excess, such as ‘until no more reacts’1
4
filter (to remove excess copper carbonate)
reject heat until dry1
heat filtrate to evaporate some water or heat to point of crystallisation
accept leave to evaporate or leave in evaporating basin1
leave to cool (so crystals form)
until crystals form1
must be in correct order to gain 4 marks
(b) Mr CuCl2 = 134.5
correct answer scores 4 marks1
moles copper chloride = (mass / Mr = 11 / 134.5) = 0.08178438661
Mr CuCO3= 123.51
Mass CuCO3 (=moles × M2= 0.08178 × 123.5) = 10.1(00)1
accept 10.1 with no working shown for 4 marks
(c)
or
11.0 × 0.7911
8.70 (g)1
accept 8.70(g) with no working shown for 2 marks
(d) Total mass of reactants = 152.51
Page 28 of 37Immanuel+College
134.5
152.5
allow ecf from step 11
88.20 (%)1
allow 88.20 with no working shown for 3 marks
(e) atom economy using carbonate lower because an additional product is made or carbondioxide is made as well
allow ecf1
[14]
(a) (i) natural gas
allow fossil fuels / biogas generator1
5
(ii) air contains oxygen1
this would react with / oxidise the hydrogen
allow this would react with / oxidise the iron
ignore nitrogen1
(iii) cooled1
ammonia condenses / liquefies (so can be separated)1
nitrogen and hydrogen (remain as gases and) are returned to the reactor
allow recycled1
(b) (i) 200 °C and 1000 atmospheres1
(ii) the reaction is reversible
allow stated as equilibrium or forward / backward reaction anywherein answer
1
forward reaction is exothermic so increased temperature lowers the yield of ammonia
allow converse1
a lower temperature would decrease rate of reaction
allow converse1
Page 29 of 37Immanuel+College
a higher pressure would increase the yield of ammonia because the forward reactionproduces the least number of (gaseous) molecules / moles
allow converse1
higher pressures would involve high cost / energy1
ignore risk / explosion
[12]
(a) any two from:
• heat water / make steam / boil water or heat / steam used in stage 1 or fromstage 3
• carbon dioxide from stage 3 used in stage 7 /to make urea
• nitrogen and / or hydrogen recycled
• ammonia and / or carbon dioxide recycled
allow unreacted material / gas recycled from stage 5 (to 4)
allow unreacted material / gas recycled from stage 8 (to 7)
NB: if neither of the last two points are awarded unreacted materialrecycled = 1 mark
2
6
(b) (i) increase yield
because (forward) reaction is exothermic
ignore references to rate1
allow because (forward) reaction gives out heat1
(ii) increase yield
ignore references to rate1
because more (gaseous) reactant molecules than (gaseous) product molecules
accept because greater volume on the left than the right1
Page 30 of 37Immanuel+College
(c) 76.9 - 77
correct answer gains 2 marks with or without workingallow 77 or 76.923…
allow 76 or 0.77 or 0.76923 for 1 mark
if answer incorrect allow 1 mark for either
or
2
[10]
x 100
x 100
(a) 2.61 / range 2.5 to 2.7
correct answer with or without or with wrong working gains 2 marks
(accept answers between 2.5 and 2.7)
if answer incorrect moles of salicylic acid = 2/138 = 0.0145 molesie 2/138 or 0.0145 gains 1 markor(180/138) × 2 gains 1 markor1 g → 180/138 = (1.304 g) gains 1 mark(not 1.304g alone)
2
7
(b) 42.1 range 40.7 to 42.3
accept correct answer with or without or with wrong working for 2marks
ecf ie (1.1 / their answer from (a)) × 100 correctly calculated gains 2marks
if answer incorrect percentage yield = 1.1 / 2.61 × 100 gains 1 mark
if they do not have an answer to part (a)orthey choose not to use their answer then:
• yield = (1.1 / 2.5) × 100 (1)
• = 44
accept 44 for 2 marks with no working2
Page 31 of 37Immanuel+College
(c) any one from:
• errors in weighing
• some (of the aspirin) lost
do not allow ‘lost as a gas’
• not all of the reactant may have been converted to product
eg reaction didn’t go to completion
allow loss of some reactants
• the reaction is reversible
accept other products / chemicals
• side reactions
ignore waste products
• reactants impure
• not heated for long enough
• not hot enough for reaction to take place1
(d) any one from:
• use lower temperature
• use less fuel / energy
ignore references to use of catalyst
• produce product faster or speed up reaction
• more product produced in a given time (owtte)
• increased productivity
• lowers activation energy1
[6]
Page 32 of 37Immanuel+College
(a) 1213.8 to 1214.3
gains 3 marks without working
correct answer not given then check working
1) moles of N2 =
1 mark for each correct step
do not penalise rounding errors in this part
2) moles of NH3 = 2 × (answer from (1)) = 71.4 mol
3) mass of NH3 = (answer from 2) × 17 = 71.4 × 17 = 1214 g3
8
= 35.7 mol
or
• 28g of N 2 → 34g of NH31 mark for each correct step
• 1g of N 2 → 3
do not penalise rounding errors in this part
• 1000 g of N 2 → 1000 × 1.214 = 1214g
allow error carried forward eg
= 1.214g NH
or
• 1000 ×
gains 2 marks if correct answer not given
1000 ×
(823.5g) 1000 × calculated correctly (1647.05g)
gains 1 mark, 2 marks if correctly calculated
gains 1 mark if or
other correct methods
look for the key ideas in the methods above
Page 33 of 37Immanuel+College
(b) 25 / 25.035 or ecf from (a)
gains 2 marks even when there is no working
incorrect answer then 304/(their answer from (a)) × 100 gains 1mark
or using figures from part (b)
27.6 / 28
gains 2 marks even when there is no working
accept 27 for 1 mark
if answers incorrect then304/1100 × 100 gains 1 mark2
(c) (i) increase yield1
reaction is exothermic
or
allow decreased yield because rate of reaction is slower /fewer collisions for 2 marks
must get both points for 2 marks1
(ii) increase yield1
plus one from:
• more (gaseous) reactant molecules than (gaseous)product molecules (owtte)
accept greater volume on the left than the right owtte
• increased rate of reaction / more collisions1
Page 34 of 37Immanuel+College
(d) any one from:
economic
• large town provides workforce
• workers do not have to travel far to the factory. (owtte)
• transport infrastructure already in place for large town. (owtte)
• factory brings prosperity to town (owtte)
• factory provides employment
• reduced tourism
• reduction in local house prices
• any other sensible economic factor linked to town1
any one from:
safety
• escape of dangerous / harmful chemicals / gases (owtte)
do not allow polluting gases unqualified
• danger of increased traffic
• risk of explosion.(owtte) /danger of high pressure
• consequences of an accident could be severe if the town is close
• any other sensible safety idea1
Page 35 of 37Immanuel+College
any one from:
environmental
• factory might be unsightly (owtte)
• screening of factory (owtte)
• loss of habitats (owtte)
• plant trees/ hedges etc on and around plant site
• pollution of water / air / soil could harm plants / animals or noise pollution
must be explained
• CO 2 is produced by burning fuels / heating
• CO 2 causes global warming / any effect of global warming
• eye sore
• any other sensible environmental factor1
[12]
(a) (i) atmosphere
or (fractional distillation of liquid) air1
(ii) eithermore (chance) of them colliding/
not just ‘faster’
coming into contactorthe volume of the product / the ammonia is less than /only half the volume of the reactants / the nitrogen and hydrogen
1
9
(iii) 3 × (1 ×2) of hydrogen→ 2 × (14 +1 ×3) of ammonia
accept 6 parts of hydrogen →34 parts of ammonia or similari.e. candidate uses the atomic masses and works correctly from theequation
1
= 225 (tonnes/t)
unit not required1
Page 36 of 37Immanuel+College
(b) (i) megapascal(s)
accept million pascal(s)1
(ii) 28 (%)
accept any answer in the range 28.0 to 28.5 inclusive1
(iii) reduce the temperature and increase the pressure
both required1
(iv) eitheruse a catalyst
accept use iron as a catalyst
accept use iron which has been more finely divided
accept use iron / catalyst with a bigger (surface) area
accept use a better catalyst1
orremove the ammonia (as it is produced)
accept react the ammonia with or dissolve the ammonia in water(as it is produced)
1
(c) ammonianitric acidphosphoric acid
all three on the left correct
ammonia potassium chloride
all three on the right correct
water or water vapour
accept ‘steam’1
[10]
Page 37 of 37Immanuel+College