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

Higher tier only

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

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N₂ + 3H₂  2NH3

Complete the equation below using the key:

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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.

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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).

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.

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

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

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.

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

 NO₂     +     O₂     +     2H₂O     →      HNO₃

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

The following pie chart shows the uses of sulfuric acid.

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.

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

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

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ammonium nitrate contains less nitrogen than urea
ammonium nitrate is better suited to British weather conditions than urea
more ammonium nitrate is absorbed by plants than urea
ammonium nitrate is more expensive than urea

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

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

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

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

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

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.

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.

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.

Name the catalyst used in the Contact Process.

Describe how concentrated sulfuric acid is made from sulfur trioxide.