Reversible Reactions, Industrial Processes & Important Chemicals (WJEC GCSE Chemistry): Exam Questions

Higher tier only

The diagram outlines the manufacture of ammonia by the Haber process.

i) Name the raw material X. .........................................

[1]

ii) The pressure used in the Haber process is 200 atm. State why a higher pressure is not used.

[1]

iii) At 450°C, the reaction is very slow. Iron is used in the process to speed up the reaction. Give the name for a substance used to speed up a chemical reaction.

[1]

iv) The reaction between nitrogen and hydrogen is represented by the equation below.

 N₂ + 3H₂  2NH3

Complete the equation below using the key:

[2]

One of the main uses of ammonia is in the manufacture of fertilisers.

The table shows the results obtained when tests were carried out on three different fertilisers A, B and C.

Give the letter of the fertiliser which is ammonium sulfate.

[1]

Letter ...........................

Ammonia reacts with chlorine to form nitrogen and hydrogen chloride.

Complete the balancing of the equation for this reaction.

2NH₃ + 3Cl₂  N₂ +  HCl

Higher tier only

Sulfuric acid is manufactured using the Contact Process. The equation represents one stage of the process.

2SO₂ (g) + O₂ (g)  2SO₃ (g)

Describe and explain all the stages in the process, including the one given above, from raw materials to the final product, sulfuric acid. 

The following table contains the names and formulae of four nitrogenous fertilisers.

Use the information in the table to answer parts (i) and (ii).

i) Give the names of all the elements present in urea.

[1]

ii) Give the name of the compound with the formula NH₄NO₃.

[1]

State why it is an advantage for a fertiliser to release its nitrogen slowly.

Describe two consequences of nitrogenous fertilisers being washed into rivers.

Another substance which is added to soil by farmers is calcium hydroxide, commonly known as slaked lime.

Give the reason why slaked lime is added to soil. 

In the Haber process, nitrogen reacts with hydrogen to give ammonia.

The following graphs show the effect of changing pressure on the yield of ammonia at 300°C and 500°C.

The table shows the percentage yield of ammonia at various pressures at 400°C.

Plot the points on the grid above and draw a suitable line.

Using the graphs, state the temperature and pressure which produce the highest yield of ammonia.

   ..................................... °C and ..................................... atm

State what conclusions can be drawn from the graphs.

i) Complete and balance the following equation for the production of ammonia.

[2]

N₂ + H₂   .......................

ii) State the meaning of in the equation in part (i).

[1]

One of the main stages in the manufacture of sulfuric acid is the reaction between sulfur dioxide and oxygen to form sulfur trioxide.

i) Write the balanced symbol equation which represents this reaction.

[3]

.................... + .................... .................... 

ii) The graph below shows how the percentage yield of sulfur trioxide changes with temperature between 300°C and 800°C.

Use the graph to find the increase in percentage yield if the temperature is reduced from 650°C to 450°C.

[2]

Increase in percentage yield = ........................ %

iii) One molecule of sulfur trioxide reacts with one molecule of sulfuric acid to form one molecule of oleum as the only product.

 Write a balanced symbol equation for this reaction.

[2]

.................... + .................... → ....................  

State what you would observe when a few drops of concentrated sulfuric acid are added to a beaker containing a small amount of sugar. Name the product left in the beaker.

Describe the benefits of the use of nitrogenous fertilisers and the problems that arise when they are washed into rivers.

Higher tier only

Ammonia is made industrially from nitrogen and hydrogen by the Haber process.

The table below shows the yield of ammonia under different pressure and temperature conditions.

i) Using only the data in the table suggest the conditions that should be chosen for the process.

[1]

Pressure .......... atmospheres          Temperature .......... °C

ii) Give the disadvantage of using a low temperature in the process and state how this problem is overcome.

[2]

iii) The actual pressure used in the process is 200 atmospheres. Apart from safety issues, suggest a disadvantage of using a higher pressure.

[1]

Ammonia is used to form nitric acid in a three-stage reaction.

i) Once the reaction in stage 1 has started there is sufficient heat to maintain the reaction. Give the term used to describe a reaction that produces heat.

[1]

ii) Balance the symbol equation below that represents the reaction taking place in stage 3.

[1]

 NO₂     +     O₂     +     2H₂O     →      HNO₃

iii) Write a balanced symbol equation for the reaction that occurs when nitric acid is added to copper(II) carbonate.

[2]

Sulfuric acid is produced by the contact process. The main stages in the process are shown below.

   Stage 1: Burning sulfur in air to produce gas A

   Stage 2: Passing gas A over a catalyst at 450°C to produce gas B

   Stage 3: Dissolving gas B in concentrated sulfuric acid to produce oleum

   Stage 4: Diluting oleum to produce sulfuric acid

i) Give the names of gases A and B.

[2]

Gas A ..............................

Gas B ..............................

ii) Which stage involves a reversible reaction?

[1]

iii) Give a reason why gas B is not dissolved directly in water during stage 3.

[1]

The following pie chart shows the uses of sulfuric acid.

i) Calculate the percentage of sulfuric acid used for making paint and pigments.

[2]

Percentage used for making paint and pigments = ........................................ %

ii) One important use of sulfuric acid is in the production of fertilisers. Complete the following word equation for the production of ammonium sulfate.

[1]

sulfuric acid + .............................. → ammonium sulfate

iii) This type of fertiliser can be washed into rivers. Explain why this is a cause for concern.

[3]

Ammonia is produced during the Haber process. The reaction is summarised in the diagram below.

Give the name of gas A.

Name catalyst B and state why it is used. 

The yield of ammonia is only 28% therefore 72% of the gases remain unreacted.

Describe what happens to these unreacted gases and state why this is important.

Higher tier only

The flow diagram outlines the manufacture of ammonia by the Haber Process followed by the production of ammonium sulfate by neutralisation.

Explain the choice of temperature used in the Haber Process and the reason why a catalyst is used.

Powdered ammonium sulfate is industrially formed by spraying sulfuric acid into a reaction chamber filled with ammonia gas. The exothermic reaction that occurs evaporates all water present in the system, forming a powdery salt.

Write a balanced symbol equation for this reaction.

In the laboratory ammonium sulfate is prepared by reacting ammonium hydroxide solution with dilute sulfuric acid.

Describe the titration method for making pure crystals of ammonium sulfate in the laboratory. Explain each stage of your method.

Fertilisers usually contain compounds of three essential elements required for healthy and productive plant growth. The table shows the properties of two nitrogenous fertilisers.

i) Which fertiliser leads to the absorption of more nitrogen from a full 2000 litre spreader? Show your working.

[2]

Fertiliser ......................................................................................................

ii) Urea is the most widely used fertiliser in the world. However, many British farmers prefer to use ammonium nitrate.

Put a tick (✓) in the box next to the statement which suggests the main reason for this.

[1]

The flow chart shows the chemical tests for the identification of the ions present in ammonium sulfate, (NH₄)₂SO₄.

i) Write a balanced symbol equation for the reaction between ammonium sulfate and sodium hydroxide.

[2]

ii) The symbol equation below represents the reaction occurring between ammonium sulfate solution and barium chloride solution.

BaCl₂(aq) + (NH₄)₂SO₄(aq)  2NH₄Cl(aq) + BaSO₄(s)

Write the ionic equation for the reaction. Include the state symbols.

[2]

.............................. + .............................. ..............................

Describe how sulfur is converted into sulfuric acid in the contact process. Include equations in your account.

Sulfuric acid is produced in industry by the contact process.

The contact process involves four stages. The first two are shown below.

   Stage 1:   sulfur + oxygen → sulfur dioxide

   Stage 2:   sulfur dioxide + oxygen  sulfur trioxide

i) Name the raw material that provides oxygen in stage 1.

[1]

ii) Describe the last two stages in the contact process (stages 3 and 4).

[2]

Stage 3: ................................................................................

Stage 4: ................................................................................

iii) Name the catalyst used in stage 2.

[1]

When concentrated sulfuric acid is added to sugar a black solid is formed.

In terms of the elements present in sugar, describe what happens during this reaction.

Higher tier only

Ammonia is produced from the reaction of nitrogen with hydrogen in the Haber process:

N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)

The forward reaction is exothermic.

The conditions normally used in the Haber process are:

• 450 ^oC

• Pressure of 200 atm

• Iron catalyst

Use your knowledge of reversible reactions and the equation to explain why these conditions are used.

An industrial manufacturer uses the following flowchart to produce fertiliser.

The first step in the process is the conversion of nitrogen and hydrogen into ammonia.

i) State the raw material used as the source of each gas.

[1]

ii) State three conditions for this conversion.

[3]

iii) Only a small percentage of the nitrogen and hydrogen is converted into ammonia. Explain how the unreacted gases are separated from ammonia.

[2]

Higher tier only

The equation for the production of ammonia is:

N₂ (g) + 3H₂ (g)  2NH₃ (g)

Calculate the maximum mass of ammonia that can be obtained from 56 tonnes of nitrogen. Show your working in moles.

Higher tier only

The main compound in the fertiliser contains 35% nitrogen and 5 % hydrogen by mass. The remainder is oxygen.

i) Determine the simplest formula of the compound.

[4]

ii) Name the main compound.

[1]

Higher tier only

A rival company produces ammonia using the same reaction but using a higher temperature and pressure.

State the advantages and disadvantages of using these conditions.

Sulfuric acid is made by the Contact Process.

In the first stage, sulfur is burned by spraying droplets of molten sulfur into air.

Suggest and explain an advantage of using this method.

In the second stage, sulfur dioxide reacts with oxygen from the air.

2SO₂ (g) + O₂ (g)  2SO₃ (g)

The reaction mixture contains 1 volume of sulfur dioxide to 1 volume of oxygen.

i) What volume of air contains 1 dm³ of oxygen?

[1]

ii) Sulfur dioxide is more expensive than oxygen. What is the advantage of using an excess of air?

[1]

Name the catalyst used in the Contact Process.

Describe how concentrated sulfuric acid is made from sulfur trioxide.