Haber Process & NPK Fertilisers (AQA GCSE Chemistry)

Exam Questions

2 hours25 questions
1a1 mark

The Haber process is a chemical process that produces ammonia.

The word equation for the reaction is:

nitrogen   +   hydrogen   rightwards harpoon over leftwards harpoon   ammonia

What does the symbol rightwards harpoon over leftwards harpoon mean?

1b1 mark

Complete the balanced symbol equation for the reaction between nitrogen and hydrogen to produce ammonia.

N2 (g)   +   ___ H2 (g)   rightwards harpoon over leftwards harpoon   ___ NH3 (g)

1c1 mark

A catalyst is used in the Haber process.

What is the purpose of a catalyst?

Tick (✓) one box.

To increase the yield of the reaction  
To increase the rate of the reaction  
To increase the amount of energy required for the reaction to occur   
To increase the overall energy change of the reaction  
1d1 mark

Circle the correct word to complete the sentence.

  The catalyst used in the Haber process is

carbon.

iron.

nickel.

1e3 marks

The reaction profile for the production of ammonia in the Haber process is shown in Figure 1.

Figure 1

aqa-gcse-10-4e-tq1e-reaction-profile-haber

Draw one line from each label, A, B and C, to the correct description of what the label represents in the reaction profile.

labels-haber

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2a2 marks

The Haber process is used to produce ammonia from nitrogen and hydrogen.

Figure 1 shows the Haber process.

Figure 1

the-haber-process

What temperature and pressure are used inside the reactor?

Temperature:   ___________________  oC  

Pressure:   ___________________ atm

2b2 marks

Nitrogen and hydrogen used in the Haber process are obtained from different sources.

Circle the correct word to complete the sentences.

  Nitrogen is obtained from

air.

water.

ammonia.

  Hydrogen is obtained from

natural gas.

alkenes.

alcohol.

2c1 mark

Ammonia is separated from the unreacted hydrogen and nitrogen in the condenser.

How is ammonia separated from the reaction mixture?

2d1 mark

The Haber process has a percentage yield of about 15% so much of the nitrogen and hydrogen is unreacted.

What happens to the unreacted nitrogen and hydrogen?

2e2 marks

Nitrogen and hydrogen are non-metals.

When they react to form an ammonia molecule, covalent bonds are formed between the atoms.

What are covalent bonds?

2f2 marks

Complete the dot and cross diagram for a molecule of ammonia.

The electrons from each atom of hydrogen have already been included.

dot-and-cross-ammonia-incomplete

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3a1 mark

The Haber process produces ammonia from nitrogen and hydrogen in the reaction shown below.

nitrogen   +   hydrogen   rightwards harpoon over leftwards harpoon  ammonia

N2 (g)   + 3H2 (g)   rightwards harpoon over leftwards harpoon   2NH3 (g)

It is a reversible reaction and the forward reaction is exothermic.

The reaction is in equilibrium in the reaction vessel. 

What is meant by 'equilibrium'?

3b1 mark

Temperature and pressure affect the position of equilibrium.

What happens to the amount of ammonia produced when the pressure is increased?

Tick (✓) one box.

Increases  
Stays the same  
Decreases  
3c1 mark

What happens to the amount of ammonia produced when the temperature is increased?

Tick (✓) one box.

Increases  
Stays the same  
Decreases  
3d1 mark

An iron catalyst is also used in the Haber process.

What is the effect on the amount of ammonia produced when a catalyst is used?

Tick (✓) one box.

Increases  
Stays the same  
Decreases  
3e1 mark

The ammonia produced in the Haber process is used as a raw material to manufacture many products.

Which is ammonia used to manufacture?

Tick (✓) one box.

Aluminium  
Sulfuric acid  
Fertilisers  
Alkenes  

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4a1 mark

The ammonia produced in the Haber process is used to produce nitrogen-based fertilisers.

One fertiliser is produced from neutralising ammonia with nitric acid.

What is the name of the compound produced?

4b4 marks

Ammonium phosphate, (NH4)3PO4, is another fertiliser that can be produced from ammonia.

In the box below, write how many atoms there are of each element in one molecule of ammonium phosphate.

Nitrogen, N  
Hydrogen, H  
Phosphorous, P  
Oxygen, O  
4c1 mark

Ammonium sulfate is also a fertiliser that can be manufactured by reacting ammonia with an acid.

Which acid would be needed?

Tick (✓) one box.

Phosphoric acid  
Sulfuric acid  
Hydrochloric acid  
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1 mark

NPK fertilisers contain the three essential elements which improve agricultural productivity.

Table 1 shows the percentages of the three elements, nitrogen, phosphorous and potassium which are contained in four different fertilisers, W, X, Y and Z.

Table 1

Percentage (%) of element in fertiliser
Fertiliser Nitrogen  Phosphorus Potassium
W 25 0 0
X 12 0 37
Y 19 22 0
Z 23 18 21

Use the information in Table 1 to state which fertiliser contains the highest total percentage of all of the essential elements?

Tick (✓) one box.

W  
X  
Y  
Z  

4e1 mark

When plants do not have sufficient amounts of the three essential elements, they do not grow as well and show visible signs.

  • Plants lacking in nitrogen can have yellow leaves
  • Plants lacking in phosphorus can be slow to grow
  • Plants lacking in potassium can have wilted leaves

Which of the fertilisers in Table 1 would be best to treat land where the plants are growing slowly and have wilted leaves?

Use the information in Table 1.

Tick (✓) one box.

W  
X  
Y  
Z  

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51 mark

What essential plant nutrients do fertilisers supply?

A phosphorus calcium nitrogen
B iron nitrogen magnesium
C nitrogen  potassium  phosphorus
D potassium calcium  nitrogen

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    1a2 marks

    The Haber process, shown in Figure 1, is used to manufacture ammonia from nitrogen and hydrogen.

    Ammonia is used to produce nitrogen-based fertilisers. 

    Figure 1

    haber-process-flowchart-with-condenser

    A mixture of gases leave the reactor.

    Explain the composition of the gases that leave the reactor. 

    1b3 marks

    The boiling points of the three gases are shown in Table 1.

    Table 1

    Gas Boiling point in oC
    Ammonia -33.3
    Hydrogen -252.9
    Nitrogen -195.8

    Explain how ammonia is separated from the mixture of gases.

    1c1 mark

    The remaining two gases of the Haber process are recycled.

    Explain why.  

    1d2 marks

    Complete and balance the equation for the reaction in the Haber process.

    ____ (g)  +  ____ (g)    __  NH3(g)

    1e3 marks

    Increasing the temperature reduces the yield of ammonia.

    Explain why. 

    1f2 marks

    Calculate the volume of ammonia produced from the complete reaction of 1700  dm 3 of hydrogen.

    Give your answer to 3 significant figures. 

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    21 mark

    Which is not true about the Haber process for making ammonia?

    • Platinum is used as a catalyst

    • The process is carried out at a temperature of about 450 oC

    • The process takes place at a pressure of about 200 atmospheres

    • Natural gas is a raw material

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    31 mark

    What does the graph show about the effect of pressure and temperature on the Haber process?

    10-4

    • Less ammonia is produced at higher pressures

    • The yield of ammonia decreases with increased temperature

    • The optimum conditions are low pressure and high temperature

    • At 500 atmospheres and 400 oC the yield of ammonia is 45%

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    4a2 marks

    In the Haber process, nitrogen and hydrogen react to produce ammonia.

    The reaction between nitrogen and hydrogen is exothermic.

    Draw a reaction profile for this reaction.

    4b1 mark

    The reaction between nitrogen and hydrogen in the Haber process is reversible.

    The graph in Figure 2 shows how the percentage yield of the product of this reaction, ammonia, varies at different temperatures and pressures.

    Figure 2 

    percentage-yield-vs-pressure-haber-process

    Suggest, using Figure 2,  the conditions that would produce the greatest yield of ammonia. 

    4c5 marks

    In the Haber process, the conditions used to produce ammonia are not those that would give the greatest yield.

    Using Figure 2, suggest and explain why. 

    4d3 marks

    Purified hydrogen and nitrogen are also passed over powdered iron in the Haber process.

    Explain why. 

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    What is the atom economy of the Haber process?

    N2 + 3H2 begin mathsize 14px style rightwards harpoon over leftwards harpoon end style2NH3

    Relative atomic masses (Ar): H = 1 N = 14

    • 82.3%

    • 17.6%

    • 25.0%

    • 100%

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    61 mark

    Which is not true about phosphate-containing rock?

    • It can be applied directly to the ground

    • It reacts with nitric acid to produce phosphoric acid and calcium nitrate

    • It reacts with sulfuric acid to produce single superphosphate

    • It reacts with phosphoric acid to produce calcium phosphate

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    71 mark

    Ammonia and sulfuric acid can react in the lab to make ammonium sulfate fertiliser.

    What is the formula of the product?

    • NH3SO4

    • NH4SO4

    • (NH4)2SO4

    • (NH3)2SO4

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    8a8 marks

    Ammonia is produced in the Haber process and is used to make fertilisers.

    Table 1 shows information about compounds used as fertilisers.

    Table 1

    Compound Cost in $ per kg Formula
    A 1.95 KCl
    B 4.75 (NH4)2HPO4
    C 2.50 NH4NO3


    Name the element in compound C which plants require to make amino acids for growth.

    8b2 marks

    Explain why compounds B and C would not be mixed to make a fertiliser.

    8c5 marks

    Phosphate rock is a source of phosphate that is used in the manufacture of fertilisers.

    Triple superphosphate is made when phosphate rock is treated with phosphoric acid.

    Describe how two other soluble salts can be produced from phosphate rock. 

    8d2 marks

    NPK fertilisers are formulations of different salts.

    Explain what is meant by the term ‘formulation’. 

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    9a1 mark

    This question is about the Haber process.

    In the Haber process, the reaction of nitrogen with hydrogen to produce ammonia (NH3) is reversible.

    Reversible reactions can reach equilibrium in a closed system.

    Explain what is meant by the term ‘closed system’.

    9b2 marks

    Give the two sources of the reactants in the Haber process. 

    9c3 marks

    Name the catalyst used in the Haber process and explain how it speeds up the reaction. 

    9d2 marks

    When the reversible reaction in the Haber process reaches equilibrium, it appears to have stopped.

    Explain why, referring to the substances involved. 

    9e3 marks

    Suggest and explain the effect of increasing the pressure on the amount of ammonia produced if the reaction of the Haber process is at equilibrium.

    You should refer to the reaction equation in your answer. 

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    1a6 marks

    Ammonia is prepared industrially from nitrogen and hydrogen in the Haber process. The equation for the reaction is:

    N2 (g)   + 3H2 (g)   rightwards harpoon over leftwards harpoon   2NH3 (g)

    The forward reaction is exothermic.

    State the conditions used in the Haber process.

    Use the equation and your knowledge of reversible reactions to explain why these conditions have been chosen for the Haber process.

    1b2 marks

    Calculate the volume of hydrogen, in dm3, required to produce 650 dm3 of ammonia, assuming the reaction goes to completion.

    1c3 marks

    A mixture of unreacted hydrogen and nitrogen together with ammonia leaves the reactor.

    The reaction mixture can be cooled to -40 oC to liquify ammonia and separate it from nitrogen and hydrogen which remain gases.

    Using this information, explain how the boiling points of ammonia, nitrogen and hydrogen compare.

    1d1 mark

    What happens to the nitrogen and hydrogen after the ammonia has been separated from the mixture?

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    2a2 marks

    Ammonia produced from the Haber process is used as a raw material to make fertilisers.

    Ammonium sulfate is a common fertiliser that can be made in the laboratory by the titration of ammonia solution with sulfuric acid.

    A student followed the method below to make ammonium sulfate.

    Step 1 Fill a burette with dilute sulfuric acid to the zero mark
    Step 2 Measure 25 cm3 of ammonia solution and pour into a conical flask
    Step 3 Add 0.5 cm3 of dilute sulfuric acid from the burette into the conical flask and swirl
    Step 4 Dip a glass rod into the solution in the conical flask and put a drop of the solution onto blue litmus paper
    Step 5 Repeat step 4 and 5 until the litmus paper just turns pink
    Step 6 Record the volume of dilute sulfuric acid added


    Explain why the student used litmus paper instead of adding an indicator to the ammonia solution to find the end point.

    2b
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    4 marks

    The balanced symbol equation for the neutralisation of ammonia solution with sulfuric acid is:

       2NH3 (aq)   +   H2SO4 (aq)   →    (NH4)2SO4 (aq)

    The student carried out the titration to make the fertiliser, ammonium sulfate.

    They found that 23.45 cm3 of 1 mol/dm3 sulfuric acid was needed to neutralise 25.0 cm3 of ammonia solution.

    Calculate the concentration of the ammonia solution.

    Give your answer to three significant figures.

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    5 marks

    Urea is another compound used by farmers.

    Urea is made from ammonia in the reaction below.

    2NH3 + CO2 rightwards harpoon over leftwards harpoon NH2CONH2 + H2O

    Compare the atom economy of urea for this reaction with the atom economy of ammonium sulfate in the reaction between sulfuric acid and ammonia.

    Relative atomic masses (Ar): H = 1;  C = 12;  N = 14;  O = 16;  S = 32

    2d
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    Ammonium nitrate, NH4NO3 is another fertiliser made from ammonia. 

    Fertilisers containing nitrogen are also known as nitrogenous fertilisers.

    Calculate the percentage by mass of nitrogen for ammonium nitrate and ammonium sulfate, (NH4)2SO4, to determine which fertiliser is the best nitrogenous fertiliser.

    Relative atomic masses (Ar):  H = 1;  N = 14;  O = 16;  S = 32

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    3a2 marks

    Ammonia is made from nitrogen gas and hydrogen gas in the Haber process.

    The equation for the reaction is:

    N2 (g)   +   3H2 (g)   rightwards harpoon over leftwards harpoon   2NH3 (g)

    Figure 1 shows how the percentage yield of ammonia depends on the temperature and pressure of the reacting mixture.

    Figure 1

    aqa-gcse-10-4h-q3a-haber-process-graph

    What temperature and pressure would produce the maximum percentage yield of ammonia?

    3b1 mark

    Typical conditions used in the Haber process are 450 oC and 200 atm.

    Use Figure 1 to determine the percentage yield of ammonia using these conditions.

    3c3 marks

    What is the effect of an increase in the temperature on the yield of ammonia?

    Explain your answer.

    3d1 mark

    A temperature of 100 oC at 200 atm gives a percentage yield of ammonia of over 98%.

    Why is this temperature not used in the Haber process?

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    4a2 marks

    Farmers use fertilisers to improve agricultural productivity.

    NPK fertilisers are one type of fertiliser that can be used.

    Why can NPK fertilisers be described as formulations and what elements do they contain which are essential for healthy crops?

    4b4 marks

    NPK fertilisers contain different compounds to provide the essential elements needed for healthy crop production.

    Many of these compounds are made by neutralisation reactions.

    Complete Table 1 which shows the acid and alkali required to make the fertilisers.

    Table 1

    Acid Alkali Fertiliser
    Nitric acid Ammonia solution  
      Calcium hydroxide Calcium phosphate
        Potassium nitrate
        Ammonium phosphate

    4c2 marks

    Phosphate rock is obtained from mining. It cannot be used directly as a fertiliser so it has to be treated with acid to produce soluble salts that can be used as fertilisers.

    Give the name of the salts produced when phosphate rock is treated with nitric acid and phosphoric acid.

    With nitric acid ________________________________________
       
    With phosphoric acid ________________________________________

    4d1 mark

    Diammonium hydrogen phosphate, (NH4)2HPO4 is a water soluble salt that can be used as a fertiliser.

    Deduce the charge on the hydrogen phosphate ion.

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    5a1 mark

    Ammonia is used as a raw material for many fertilisers.

    Figure 1 shows a flowchart for the manufacture of  fertiliser A.

    Figure 1

    production-ammonium-phosphate

    What is the name of fertiliser A?

    5b1 mark

    Some compounds that contain potassium are mined and can be used directly as a fertiliser.

    Name one of these compounds.

    5c2 marks

    Table 1 shows information about three compounds that are used as fertilisers.

    Table 1

    Fertiliser Formula Cost in £ per kg
    X (NH4)2HPO4 0.350
    Y NH4NO3 0.220
    Z KCl 0.235

    A farmer uses fertilisers X and Z to fertilise a field.

    Give an advantage and a disadvantage to using both fertilisers.

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    The farmer uses fertiliser Y on a different field.

    400 kg of fertiliser Y covers an area of 0.1 km2.

    How much would it cost to fertilise a field with fertiliser Y which has an area of 0.03 km2?

    Use Table 1.

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