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C3 3.5 The production of Ammonia
Using Exam pro items to support successful outcomes
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• Learners will be able to test their progress against learning outcomes using questions from past AQA GCSE examinations
• C3 3.5
Foundation Tier QSP 3F 04
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• C3 3.5
. Ammonia is used in the production of fertilisers. The flow diagram shows the main stages in the manufacture of ammonia.
Study the flow diagram and then answer the questions.
(a) (i) Name gas X and name gas Y.
Gas X is ............................... Gas Y is ............................... (2)
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• C3 3.5
(ii) Draw a ring around the correct answer to complete the sequence.
cooled
In the condenser the mixture is heated to separate ammonia as a liquid.
oxidised
(1)
(b) The ammonia is separated as a liquid from the unreacted gases.
Suggest two reasons why the unreacted gases are recycled.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................ (2)
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• C3 3.5
(c) The graph shows the percentage of ammonia made at different temperatures and pressures.
Study the graph and then answer the questions.
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• C3 3.5
(i) Draw a ring around the correct answers to complete the sentence.
To make the greatest percentage yield of ammonia
the temperature should be
low
medium
high
and the pressure
should be
low
medium
high
(2)
(ii) What is the percentage yield of ammonia at a temperature of 450°C and at a pressure of 200 atmospheres?
................................................ % (1)
(iii) Ammonia is often made at a temperature of 450°C and at a pressure of 200 atmospheres.
Suggest two reasons why it is economical to make ammonia using these conditions.
...............................................................................................................
...............................................................................................................
...............................................................................................................
............................................................................................................... (2)
(Total 10 marks)
Mark scheme- Foundation
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• C3 3.5
Q 1 Answer Extra Information Mark (a) (i) (gas X) nitrogen/N2
(gas Y) hydrogen/H2
11
(a) (ii) cooled 1
(b) any two from:• save materials/resources• save energy/fuels• reduce costs• reduce waste
2
(c) (i) lowhigh
11
(c) (ii) 40(%) 1
Mark scheme- Foundation
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• C3 3.5
Q 2 Answer Extra Information Mark
(c) (iii)
any two from:• using these conditions the yield is still high• higher pressures would increase yield but energycosts would be higherorhigher pressures would increase yield but wouldmake the plant expensive to build• the temperature of 450 °C would not need alot of energyorat 450 °C the reaction would be faster than at lowertemperatures
2
Total 10
Higher Tier QCJ 99 H2 08
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• C3 3.5
The Haber process is used to make ammonia NH3. The table shows the percentage yield of ammonia at different temperatures and pressures.
PRESSURE (ATMOSPHERES)
PERCENTAGE (%) YIELD OF AMMONIA AT 350°C
PERCENTAGE (%) YIELD OF AMMONIA AT 500°C
50 25 5
100 37 9
200 52 15
300 63 20
400 70 23
500 74 25
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• C3 3.5
(i) Use the data in the table to draw two graphs on the grid below. Draw one graph for a temperature of 350°C and the second graph for a temperature of 500°C. Label each graph with its temperature.
(4)
(ii) Use your graphs to find the conditions needed to give a yield of 30% ammonia.
................................ °C and .............................. atmospheres (1)
(iii) On the grid sketch the graph you would expect for a temperature of 450°C. (1
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• C3 3.5
(b) (i) This equation represents the reaction in which ammonia is formed.
N2(g) + 3H2(g) 2NH3(g) + heat
What does the symbol in this equation tell you about the reaction?
........................................................................................................................... (1)
(ii) Use your graphs and your knowledge of the Haber process to explain why a temperature of 450°C and a pressure of 200 atmospheres are used in industry.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
........................................................................................................................... (5)
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• C3 3.5
(c) (i) Ammonium nitrate is one type of artificial fertiliser. Calculate the relative formula mass of ammonium nitrate NH4NO3. (Relative atomic masses: H = 1, N = 14, O = 16.)
...........................................................................................................................
........................................................................................................................... (1)
(ii) Use your answer to part (c)(i) to help you calculate the percentage by mass of nitrogen present in ammonium nitrate NH4NO3.
...........................................................................................................................
........................................................................................................................... (2)
(Total 15 marks)
Mark scheme- Higher
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• C3 3.5
Q 1 Answer Extra Information Mark(a) (i)
both scales
plots for 350°Cplots for 500°Clines of best fit
(must be sensible) (use at least half the paper ) (to accuracy of +/- 1/2 square)(to accuracy of +/- 1/2 square)(sensible smooth curves) (ignore below 50 atm.) (must not join the dots and each curve must be a single line)
4
(a) (ii)
read accurately from their graph (must be 350 °C and pressure readto +/– half square from their graph)for one mark
1
(a) (iii)
smooth curve drawn between 350oC and 500 °C - must be of similar shape to the other curves - a dashed line would be accepted here but would not be accepted for part (i)
1
(b)(i) reversible reaction (owtte) / equilibrium / equilibria / reaction goes in both directions etc.
1
Mark scheme- Higher
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• C3 3.5
Q 2 Answer Extra Information Mark
b) (ii)
effect of temperature (max. 2 marks) best yield at low temperature / poor yield at high temperaturereaction too slow at low temperature / fast at high temperature effect of pressure (max. 2 marks) high yield at high pressure (owtte) / low yield at low pressureideas to do with cost / safety factor of using higher pressuresevaluation (max. 2 marks) formation of ammonia favoured at low temperature becausereaction is exothermic formation of ammonia favoured at high pressure because more reactant molecules than product moleculesactual temperature and / or pressure used are a compromise between good yield and reasonable rate ammonia removed/ unreacted nitrogen and hydrogen recycled so rate more importantthan yield catalyst used (not a wrongly named catalyst)for 1 mark each
maximum of 2 marks from each section up to a maximum total of 5
(c) (i)
NH4NO3 = 14 + (4 × 1) + 14 + (3 × 16) = 80 (ignore units) 1
(c) (ii)
look for (28/80) for first markbut 35% special case of (14/80 × 100 = 17.5%) gains one markgains 2 marks
ecf (error carried forward from part (i) (% sign not needed)
2
Total 15
• C3 3.5
