Improving Processes & Products (OCR GCSE Chemistry A (Gateway))

This question is about the corrosion of metals.

A student investigates the rusting of iron.

Fig. 16.1 shows the experiments she sets up.

Write about what the student would observe in each tube after one week.

Explain the observations.

Tube A ........................................

Tube B ........................................

Tube C .........................................

Another student buys a new bicycle. The bicycle chain is made of iron.

The student decides to oil the chain to prevent it from rusting, as shown in Fig. 16.2.

Explain why oiling the chain will prevent the iron from rusting.

A galvanised iron bucket is made of iron coated with a layer of zinc.

After years of use, the zinc coating has become scratched.

The iron below the zinc has been exposed but the iron has not rusted.

Explain why the iron has not rusted.

This question is about the extraction of metals.

When iron oxide is heated with carbon, iron is made.

i) Complete the word equation for this reaction.

iron oxide + carbon ................................... + ...................................

[1]

ii) Iron oxide is reduced during this reaction.

Explain how you can tell that iron oxide is reduced.

[1]

Look at the reactivity series of some metals. Carbon is also included.

i) Zinc is usually extracted from zinc oxide by heating zinc oxide with carbon. Explain why. Use the reactivity series to help you.

[1]

ii) Aluminium is extracted from aluminium oxide by electrolysis. Explain why. Use the reactivity series to help you.

[1]

The table shows some information about aluminium and zinc.

Suggest two reasons why it could be more important to recycle zinc than aluminium.

Use information from the table to help you.

1 ................................................

2 ................................................

Aluminium alloys are often used to build aircraft.

A sample of an aluminium alloy contains 1.28 g of magnesium and 43.70 g of aluminium only.

Calculate the percentage of magnesium in this alloy.

Give your answer to 3 significant figures.

Percentage of magnesium = ..................................................... %

This question is about metals and alloys.

The table gives information about some alloys.

Complete the table.

Choose your answers from the list.

Aluminium and copper
Aluminium and iron
Copper and tin
Copper and zinc
Copper and lead
Lead and zinc

Solder can be used to join metals together. A hot soldering iron is used to melt the solder.

The table gives some information about solder, copper and tin.

Solder is better than copper or tin for joining metals together.

Suggest why. Use the information in the table.

Steel is an alloy containing iron. 

Complete the word equation for the corrosion of iron.

Iron + ......................... + ......................... → .....................................

i) Iron can be plated with a layer of zinc to prevent it corroding.

This is called galvanizing.

Explain how galvanizing prevents iron from corroding.

[2]

ii) Iron can also be plated with a layer of tin to prevent it corroding.

Describe a disadvantage of tin plating for preventing corrosion.

[1]

This question is about properties of materials.

Police bullet-resistant vests could be made from steel or Kevlar®.

The table shows some information about steel and Kevlar®.

Describe and explain two reasons why bullet-resistant vests are made from Kevlar® instead of steel.

1 ..................................................................

2 ..................................................................

Higher Only

Look at the structure of Kevlar®.

What type of molecule is Kevlar®?

Nanoparticles are being used to make a material that is better than Kevlar® at resisting bullets. Nanoparticles are often made of silicon dioxide. A silicon dioxide nanoparticle has a diameter of 18 nm. The diameter of a silicon atom is 0.22 nm.

i) Estimate how many times larger the silicon dioxide nanoparticle is, compared to a silicon atom.

Give your answer to 1 significant figure.

Number of times larger = ......................................................

[3]

ii) Silicon dioxide is used as a catalyst. Suggest why 1 g of silicon dioxide is more effective as a catalyst when used as nanoparticles rather than as a powder.

[3]

This question is about the properties of materials.

Look at the table. It shows information about two materials.

Electrical cables are made of metal wires surrounded by a polymer coating.

Explain why

• the wire is made of metal

• the metal wire is coated with a polymer.

Use information from the table in your answer.

Aluminium is a metal.

Aluminium is extracted from an ore called bauxite.

Electrolysis is used to extract the aluminium.

Use the reactivity series to explain why aluminium cannot be extracted from bauxite by heating the bauxite with carbon.

Drinks cans are often made from aluminium.

4.0 kg of bauxite makes 1.0 kg of aluminium.

285 000 kJ of energy is needed to make 1.0 kg of aluminium from bauxite.

Aluminium can be recycled.

4.0 kg of recycled aluminium makes 3.8 kg of aluminium.

14 250 kJ of energy is needed to produce 1.0 kg of aluminium from recycled aluminium.

i) Describe how aluminium is recycled.

[2]

ii) Describe and explain two advantages of recycling aluminium. Use the information in the question in your answer.

[3]

The Haber process is used to manufacture ammonia, NH₃.

Ammonia is used to make fertilisers, which farmers use on their crops.

Explain why fertilisers are so important in the agricultural production of crops.

Ammonium sulfate is a fertiliser made from ammonia and sulfuric acid.

The diagram shows the stages in the industrial production of ammonium sulfate.

Complete the diagram to show the raw materials in the production of ammonium sulfate.

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

Ammonium nitrate is made by reacting ammonia with nitric acid.

NH₃ + HNO₃ → NH₄NO₃

i) Calculate the mass of ammonium nitrate that could be made from 25.5 tonnes of ammonia. A_r: H = 1.0, N = 14.0, O = 16.0

 Mass of ammonium nitrate = ................................... tonnes
[3]

ii) A student makes some ammonium nitrate in the laboratory. He predicts that he should make 12.5 g of ammonium nitrate. His percentage yield is 80%. Calculate the actual mass of ammonium nitrate that the student makes.

Actual mass of ammonium nitrate = ........................................ g
[2]

A student investigates the corrosion of different metals.

• She places a small strip of each metal in different samples of air.

• She leaves the metals for one week before collecting her results.

Look at her table of results.

Suggest, with a reason, one change to the experimental procedure that would improve the quality of the results.

Explain the conclusions that can be made from her results.

Aluminium is extracted from its ore using electrolysis.

Copper is extracted from its ore by heating with carbon.

Explain why different methods are used to extract aluminium and copper.

Molten aluminium oxide contains Al³⁺ and O^2– ions.

The electrolysis of molten aluminium oxide makes aluminium and oxygen.

i) Write the balanced half-equation for the reaction that happens at the cathode.

Use the symbol e^– to represent an electron.

[1]

ii) Solid aluminium oxide cannot be electrolysed.

Explain why.

[1]

Copper is also made by electrolysis of copper sulfate solution.

Look at the diagram of the apparatus used in this electrolysis.

Describe what you would see at each electrode.

At the anode: ..................................................................

At the cathode: ...............................................................

Higher Only

Ammonium sulfate, (NH₄)₂SO₄, is a fertiliser.

Ammonium sulfate can be manufactured from ammonia and sulfuric acid.

Sulfuric acid is manufactured in a series of steps.

Step 1:

Sulfur is burnt in oxygen to produce sulfur dioxide.

Step 2, The Contact Process:

Sulfur dioxide is reacted with oxygen to produce sulfur trioxide. This takes place in the presence of a vanadium(V) oxide catalyst at a pressure of 2 atmospheres and at about 450˚C.

Step 3:

Sulfur trioxide is reacted with water to produce sulfuric acid.

Write balanced symbol equations for each step of this process.

Step 1: .....................................................................

Step 2: .....................................................................

Step 3: .....................................................................

Ammonium sulfate is a salt.

It is manufactured using the reaction between the alkali ammonia and sulfuric acid. 

2NH₃ + H₂SO₄ → (NH₄)₂SO₄ 

What type of reaction is this?

A sample containing 17.0 g of ammonia completely reacts with sulfuric acid.

A mass of 66.0 g of ammonium sulfate is made.

Show that the maximum mass of ammonium sulfate that can be made from 51.0 g of ammonia is 198.0 g.

A student has a solution of ammonium sulfate.

Describe how he can obtain a pure dry sample of ammonium sulfate.

Iron rusts when it gets wet.

The word equation for rusting is 

iron + water + oxygen → rust (hydrated iron(III) oxide)

Balance the symbol equation for the formation of rust. 

……Fe (s) + 6H₂O (l) + ……O₂ (g) → 2Fe₂O₃•3H₂O (s)

i) Calculate the percentage by mass of iron in rust.

Give your answer to 2 decimal places.

Relative formula mass of rust = 213.6

Answer = ………………………………… %

[2]

ii) A 1.0 kg iron bar is left outside in the rain to rust.

A student predicts that the mass of the bar will increase by no more than 0.8 kg if it completely turns to rust.

Calculate the mass of rust produced, if the 1.0 kg iron bar completely turns to rust, to see if the student is correct.

Give your answer to the nearest gram.

Answer = ………………………………… g

Is the student’s prediction correct and why?

[3]

Iron rusts when it gets wet.

The word equation for rusting is 

iron + water + oxygen → rust (hydrated iron(III) oxide)

Balance the symbol equation for the formation of rust. 

……Fe (s) + ……H₂O (l) + ……O₂ (g) → ……Fe₂O₃•3H₂O (s)

A 1.0 kg iron bar is left outside in the rain.

• All of the iron turns to rust.

• The rust forms at a rate of 60 g per day.

Calculate how long it will take for the iron bar to turn completely to rust.

Give your answer to the nearest day.

Answer = ………………………………… days

In the Haber process nitrogen gas, N₂, reacts with hydrogen gas.

Ammonia, NH₃, is made. The reaction is a reversible reaction.

Write the balanced symbol equation for the reaction.

Higher Only

The conditions used to make ammonia in the Haber process are:

• a pressure of 200 atmospheres

• a temperature of 450°C.

The reaction is an exothermic reaction. A company making ammonia increases the temperature used to 550°C.

i) What happens to the rate of the reaction when the temperature is increased?

[1]

ii) The company thinks that the increase in temperature will increase the yield of ammonia.

Is the company correct? Explain your answer.

[2]

Higher Only

The company wants to reduce the cost of making the ammonia.

They decide to reduce the pressure used to 150 atmospheres.

Write about two disadvantages of using a lower pressure to make ammonia.

Ammonia is used to make fertilisers such as ammonium sulfate.

A student makes some ammonium sulfate crystals in a laboratory.

She uses a titration method, as shown in the diagram.

She adds an indicator to ammonia solution in a conical flask. She then adds dilute sulfuric acid from a burette until the indicator changes colour.

The student then crystallises the solution. She is left with impure ammonium sulfate crystals.

i) What should the student have done to obtain pure ammonium sulfate crystals?

[2]

ii) In industry the same reaction is used to make ammonium sulfate. The method used is different. Give one reason why the laboratory method to make ammonium sulfate is not used in industry.

[1]

Ammonium sulfate, (NH₄)₂SO₄, is a fertiliser.

Ammonium sulfate can be manufactured from ammonia and sulfuric acid.

The Haber Process is used to manufacture ammonia.

Explain the importance of the Haber Process in agriculture.

Higher Only

The Contact Process is used to manufacture sulfuric acid. 

• The Contact Process involves the reaction between sulfur dioxide and oxygen.

• The conditions used are 450 °C and about 10 atmospheres pressure.

i) If the temperature is increased to 500 °C the rate of reaction changes.

Describe and explain this change in rate of reaction.

[2]

ii) If the pressure is reduced to 5 atmospheres the rate of reaction changes.

Describe and explain this change in rate of reaction.

[2]

Ammonium sulfate is a salt.

It is made using the reaction between the alkali, ammonia, and sulfuric acid. 

2NH₃ + H₂SO₄ → (NH₄)₂SO₄

i) Describe how a sample of solid ammonium sulfate could be prepared in a laboratory starting from a solution of ammonia and sulfuric acid. Explain why this method is not suitable to be used industrially.

[4]

ii) Calculate the maximum mass of ammonium sulfate that can be made from 51 tonnes of ammonia.

Answer = …………………………………. tonnes

[2]

A student investigates the reactivity of four metals, A, B, C and D.

He adds a small piece of each metal to cold water.

He then adds a small piece of each metal to dilute hydrochloric acid.

Look at his results.

Write down the order of reactivity of the four metals A, B, C and D

 ............................................... most reactive

 ................................................least reactive

Higher Only

The piece of metal C used by the student produces 30 cm³ of hydrogen gas when it reacts with the dilute hydrochloric acid at room temperature and pressure.

i) Calculate the number of moles of hydrogen gas produced. One mole of any gas occupies 24 dm³ at room temperature and pressure.

Moles of hydrogen gas = ......................................................... [2]

ii) Use your answer from (b)(i) to calculate the mass of hydrogen gas produced.

Mass of hydrogen gas = ...................................................... g [1]

Higher Only

Chromium metal, Cr, reacts with nickel sulfate solution, NiSO₄. Solid nickel is made.

Two possible equations for this reaction are:

Equation 1    Cr + NiSO₄ → CrSO₄ + Ni

Equation 2    2Cr + 3NiSO₄ → Cr₂(SO₄)₃ + 3Ni

10.40 g of chromium metal reacts with excess nickel sulfate solution to make 17.61 g of nickel.

Deduce which equation, 1 or 2, represents the reaction which takes place.

A_r : Cr = 52.0, Ni = 58.7

Higher Only

Bioleaching is one method used to extract copper from ores.

Reactions involving bacteria slowly convert copper sulfide to a mixture of copper sulfate solution and sulfuric acid.

i) Describe two advantages of extracting copper using bioleaching instead of traditional mining.

[2]

ii) Suggest one reason why the sulfuric acid produced during bioleaching may be harmful to the environment.

[1]