Extraction of Metals (Cambridge (CIE) IGCSE Chemistry)

Separate: Chemistry and Extended Only

Aluminium is an important metal with a wide range of uses.

Aluminium is obtained by the electrolysis of aluminium oxide dissolved in molten cryolite.

i) Solid aluminium oxide is a poor conductor of electricity. It conducts either when molten or when dissolved in molten cryolite. Explain why.

 [2]

ii) Why is a solution of aluminium oxide in molten cryolite used rather than molten aluminium oxide?

[1]

iii) Explain why the carbon anodes need to be replaced periodically.

[1]

iv) One reason why graphite is used for the electrodes is that it is a good conductor of electricity. Give another reason.

[1]

Aluminium is used to make food containers because it resists corrosion.
Explain why it is not attacked by the acids in food.

Aluminium is used for overhead power (electricity) cables which usually have a steel core.

i) Give two properties of aluminium which make it suitable for this use.

[2]

ii) Explain why the cables have a steel core.

[1]

Aluminium was first isolated in 1827 using sodium.

AlCl₃ + 3Na → Al + 3NaCl

Aluminium, obtained by this method, was more expensive than gold.

Suggest an explanation why aluminium was so expensive.

Separate: Chemistry and Extended Only

The modern method for extracting aluminium is the electrolysis of a molten electrolyte, aluminium oxide dissolved in cryolite. The aluminium oxide decomposes.

2Al₂O₃  → 4Al + 3O₂

i) Both electrodes are made of carbon.

Give two reasons why the oxide is dissolved in cryolite.

[2]

ii) Complete the ionic equation for the reaction at the anode.

.......... O^2– → O₂ + ......... e^-

[2]

iii) Why do the carbon anodes need to be replaced frequently?

[1]

The electrolysis of a molten electrolyte is one method of extracting a metal from its ore.

Other methods are the electrolysis of an aqueous solution and the reduction of the oxide by carbon.

Explain why these last two methods cannot be used to extract aluminium.

electrolysis of an aqueous solution ...................................................................................................

using carbon .....................................................................................................

Complete the labelling of the diagram.

Separate: Chemistry and Extended Only

The ions that are involved in the electrolysis are Al³⁺ and O^2-.  

i) Write an equation for the reaction at the cathode.

[2]

ii) Explain how carbon dioxide is formed at the anode.

[2]

Give an explanation for each of the following.  

i) Aluminium is used extensively in the manufacture of aircraft.

[1]

ii) Aluminium is used to make food containers.

[2]

iii) Aluminium electricity cables have a steel core.

[1]

Iron is extracted from its ore, hematite, in a blast furnace.

Substances added to the furnace are:

• Iron ore, hematite, containing impurities such as silica, SiO₂

• Air

• Coke, C

• Limestone, CaCO₃

Substances formed in the blast furnace are:

• Molten iron

• Molten slag

• Waste gases such as carbon dioxide

State the two functions of the coke used in the blast furnace.

Write an equation for the conversion of hematite, Fe₂O₃, to iron.

Explain how the silica impurity is removed and separated from the molten iron.

The molten iron from the furnace is impure. It contains impurities which include the element carbon. Explain how the carbon is removed. Include an equation in your answer.

Iron from the Blast Furnace is impure. It contains about 5% of impurities, mainly carbon, sulfur, silicon and phosphorus, which have to be removed when this iron is converted into steel.

Explain how the addition of oxygen and calcium oxide removes these impurities. Include an equation for a reaction of oxygen and a word equation for a reaction of calcium oxide in this process.

Mild steel is the most common form of steel. Mild steel contains a maximum of 0.3% of carbon.

High carbon steel contains 2% of carbon. It is less malleable and much harder than mild steel.

i) Give a use of mild steel.

[1]

ii) Suggest a use of high carbon steel.

[1]

iii) Explain why metals are malleable.

[3]

iv) Suggest an explanation why high carbon steel is less malleable and harder than mild steel.

[2]

Separate: Chemistry and Extended Only

Aluminium is obtained by the reduction of aluminium ions to aluminium atoms.

Write an ionic equation for the reduction of an aluminium ion to an aluminium atom.

Separate: Chemistry and Extended Only

The original method of extracting aluminium involved the reduction of aluminium chloride using the reactive metal sodium. Aluminium obtained by this method was very expensive due to the high cost of extracting sodium from sodium chloride.

i) Complete the equation for this reduction.

AlCl₃ + .......Na → ........... + ...........

[2]

ii) How can sodium metal be obtained from sodium chloride?

[2]

Separate: Chemistry and Extended Only

In the modern method, aluminium is obtained by the electrolysis of aluminium oxide (alumina) dissolved in molten cryolite, Na₃AlF₆.

i) The major ore of aluminium is impure aluminium oxide. What is the name of this ore?

[2]

ii) This ore is a mixture of aluminium oxide, which is amphoteric, and iron(III) oxide which is basic.

Explain how these two oxides can be separated by the addition of aqueous sodium hydroxide.

[2]

iii) Give two reasons why the electrolyte contains cryolite.

[2]

iv) The mixture of gases evolved at the positive electrode includes:

carbon dioxide
carbon monoxide
fluorine
oxygen

Explain the presence of these gases in the gaseous mixture formed at the positive electrode. Include at least one equation in your explanation.

[4] 

Extended Only

A major use of aluminium is the manufacture of pots and pans. One reason for this is its resistance to corrosion.

i) xplain why aluminium, a reactive metal, is resistant to corrosion.

[1]

ii) Suggest two other reasons why aluminium is suitable for making pots and pans.

[2]

Iron from a blast furnace contains about 5% of the impurities – carbon, silicon, phosphorus and sulfur. Most of this impure iron is used to make steels, such as mild steel, and a very small percentage is used to make pure iron.

i) Calcium oxide and oxygen are used to remove the impurities from the iron produced in the blast furnace.

State how these chemicals are manufactured.

calcium oxide .........................
oxygen .................................

[3] 

ii) Describe how these two chemicals remove the four impurities. Include at least one equation in your answer.

[5] 

i) Describe the structure of a typical metal such as iron. You may include a diagram.

[2]

ii) Explain why pure iron is malleable.

[2]

iii) Mild steel is an alloy of iron and carbon. Suggest why mild steel is harder than pure iron.

[2]

Iron from the blast furnace is impure. It contains 5% of impurities, mainly carbon, sulfur, silicon and phosphorus. Almost all of this impure iron is converted into the alloy, mild steel.

 i) State a use of mild steel.

[1] 

ii) Name and give a use of another iron-containing alloy.

[2] 

The oxides of carbon and sulfur are gases. The oxides of silicon and phosphorus are not.

Explain how these impurities are removed from the impure iron when it is converted into mild steel.

Iron is extracted from its ore, hematite, in the blast furnace.

The temperature inside the blast furnace can rise to 2000 °C. Write an equation for the exothermic reaction which causes this high temperature.

Carbon monoxide is formed in the blast furnace. This reduces the ore hematite, Fe₂O₃, to iron.

i) Explain how carbon monoxide is formed in the blast furnace.

[2]

ii) Write an equation for the reduction of hematite by carbon monoxide.

[2]

Explain why it is necessary to add limestone, calcium carbonate, to the blast furnace. Include an equation in your explanation.

Extended Only

Most of the iron from the blast furnace is converted into mild steel. A method of preventing the steel from rusting is coating it with zinc.

i) What is the name of this method of rust prevention?

[1] 

ii) Explain, using the idea of electron transfer, why zinc-coated steel does not rust even when the coating is scratched and the steel is in contact with oxygen and water.

[2] 

Extended Only

No one knows where iron was first isolated. It appeared in China, the Middle East and in Africa. It was obtained by reducing iron ore with charcoal.

Complete the following equation.

Extended Only

In 1705 Abraham Darby showed that iron ore could be reduced using coke in a blast furnace.

i) The temperature in the furnace rises to 2000 °C. Write an equation for the exothermic reaction that causes this high temperature.

[1] 

ii) In the furnace, the ore is reduced by carbon monoxide. Explain how this is formed.

[2] 

Extended Only

The formation of slag removes an impurity in the ore.

Write a word equation for the formation of the slag.

Extended Only

Stainless steel is an alloy of iron. It contains iron, other metals and about 0.5% of carbon.

i) State a use of stainless steel.

[1] 

ii) Name a metal, other than iron, in stainless steel.

[1] 

iii) The iron from the blast furnace is impure. It contains about 5% of carbon and other impurities, such as silicon and phosphorus.

Describe how the percentage of carbon is reduced and the other impurities are removed.

[4]

Separate: Chemistry Only

One of the methods used to prevent iron or steel from rusting is to electroplate it with another metal, such as tin. Complete the following.

The anode is made of ............................................... 

The cathode is made of ............................................. 

The electrolyte is a solution of ...................................

A list of symbols and formulae is shown.

Which symbol or formula represents a compound produced by the thermal decomposition of calcium carbonate?

The diagram shows part of the structures of caesium chloride and carbon dioxide.

Explain why caesium is not extracted from caesium oxide by heating with carbon.

This question is about oxides.

The names of eight substances are given.

 State which substance is the main constituent of bauxite.

Give the name of the process that is used to extract aluminium from aluminium oxide.

The table shows how easy it is to reduce four metal oxides with carbon. 

 Use the information in the table to put the four metals in order of their reactivity.

Put the least reactive metal first. 

Zinc is extracted from an ore called zinc blende, which consists mainly of zinc sulfide, ZnS. The zinc sulfide in the ore is first converted into zinc oxide.

Zinc oxide is converted into zinc. Zinc oxide and coke are fed into a furnace. Hot air is blown into the bottom of the furnace. The process is similar to the extraction of iron from iron oxide in a blast furnace.

Zinc has a melting point of 420 °C and a boiling point of 907 °C. The temperature inside the furnace is over 1000 °C.

 i) Explain how zinc oxide is converted into zinc. Your answer should include details of how the heat is produced and equations for all the reactions you describe.

[3]

ii) Explain why the zinc produced inside the furnace is a gas.

[1]

iii) State the name of the physical change for the conversion of gaseous zinc into molten zinc.

[1]

Extended Only

Rusting of steel can be prevented by coating the steel with a layer of zinc.

Explain, in terms of electron transfer, why steel does not rust even if the layer of zinc is scratched so that the steel is exposed to air and water.

Separate: Chemistry and Extended Only

When a sample of steel is added to dilute hydrochloric acid, an aqueous solution of iron(II) chloride, FeCl₂, is formed.

When a sample of rust is added to dilute hydrochloric acid, an aqueous solution of iron(III) chloride, FeCl₃, is formed.

i) Aqueous sodium hydroxide is added to the solutions of iron(II) chloride and iron(III) chloride.

Complete the table below, showing the observations you would expect to make.

[2]

Solutions of iron(II) chloride and iron(III) chloride were added to solutions of potassium iodide and acidified potassium manganate(VII). The results are shown in the table.

ii) What types of substance cause potassium iodide solution to turn from colourless to brown?

[1]

iii) What types of substance cause acidified potassium manganate(VII) solution to turn from purple to colourless?

[1]

iv) Which ion in iron(III) chloride solution causes potassium iodide solution to turn from colourless to brown?

[1]

v) Which ion in iron(II) chloride solution causes acidified potassium manganate(VII) solution to turn from purple to colourless?

[1]

Extended Only

For centuries, iron has been extracted from its ore in the blast furnace. The world production of pig iron is measured in hundreds of million tonnes annually.

The following raw materials are supplied to a modern blast furnace.

• iron ore which is hematite, Fe₂O₃

• limestone which is calcium carbonate

• carbon in the form of coke

• air

Describe the essential reactions in the blast furnace. Each of the four raw materials must be mentioned at least once.

Give the equation for the reduction of hematite.

Extended Only

Each year, blast furnaces discharge millions of tonnes of carbon dioxide into the atmosphere. This will increase the percentage of atmospheric carbon dioxide.

i) Explain why this increased percentage of carbon dioxide may cause problems in the future.

[2]

ii) Until the early eighteenth century, charcoal, not coke, was used in the blast furnace. Charcoal is made from wood but coke is made from coal. Explain why the use of charcoal would have a smaller effect on the level of atmospheric carbon dioxide

[2]

iii) A method being developed to produce iron with lower emissions of carbon dioxide is by electrolysis. Hematite, Fe₂O₃, is dissolved in molten lithium carbonate and electrolysed. The ore is spilt into its constituent elements. Write an equation for the reaction at the negative electrode (cathode). Complete the equation for the reaction at the positive electrode (anode).

........O^2– → ............... + ...............

[3]

Separate: Chemistry and Extended Only

Aluminium is extracted by the electrolysis of a molten mixture of alumina, which is aluminium oxide, and cryolite.

Alumina is obtained from the main ore of aluminium.

 i) Name this ore.

[1]

ii) Explain why it is necessary to use a mixture, alumina and cryolite, rather than just alumina.

[2]

iii) Copper can be extracted by the electrolysis of an aqueous solution.

Suggest why the electrolysis of an aqueous solution cannot be used to extract aluminium.

[2]

Separate: Chemistry and Extended Only

The ions which are involved in the electrolysis are Al³⁺ and O^2–. The products of this electrolysis are given on the diagram.

Explain how they are formed. Use equations where appropriate.

The uses of a metal are determined by its properties.

 i) Foods which are acidic can be supplied in aluminium containers.

Explain why the acid in the food does not react with the aluminium.

[1]

ii) Explain why overhead electrical power cables are made from aluminium with a steel core.

[3]

Extended Only

Iron is extracted from its ore, hematite, in the blast furnace.

Describe the reactions involved in this extraction. Include one equation for a redox reaction and one for an acid/base reaction.

Separate: Chemistry and Extended Only 

Aluminium and iron are extracted from their ores by different methods.

Aluminium is extracted from its purified oxide ore by electrolysis.

What is the name of the ore of aluminium which consists mainly of aluminium oxide?

Separate: Chemistry and Extended Only

The electrodes are both made of the same substance.

Name this substance.

Separate: Chemistry and Extended Only

Aluminium oxide is dissolved in molten cryolite before it is electrolysed.

Give two reasons why aluminium oxide dissolved in molten cryolite is electrolysed rather than molten aluminium oxide alone.

Separate: Chemistry and Extended Only

Write the ionic equations for the reactions at the electrodes in this electrolysis.

Anode (positive electrode)

Cathode (negative electrode)

Iron is extracted from its oxide ore by reduction using carbon in a blast furnace.

i) Place the elements aluminium, carbon and iron in order of reactivity with the least reactive element first.

[1]

ii) Use your answer to (e)(i) to explain why iron is extracted by reduction using carbon but aluminium is not.

[1]

What is the name of the ore of iron which consists mainly of iron(III) oxide?

Extended Only

Write balanced equations for the reactions occurring in the blast furnace which involve

i) The complete combustion of coke (carbon)

[1]

ii) The production of carbon monoxide from carbon dioxide

[1]

iii) The reduction of iron(III) oxide

[1]

iv) The formation of slag

[1]

Iron is extracted from the ore hematite in the Blast Furnace.

The coke reacts with the oxygen in the air to form carbon dioxide.

C + O₂ → CO₂

i) Explain why carbon monoxide is formed higher in the Blast Furnace.

[2]

ii) Write an equation for the reduction of hematite, Fe₂O₃, by carbon monoxide.

[2]

Limestone decomposes to form two products, one of which is calcium oxide.

 i) Name the other product

[1]

 ii) Calcium oxide reacts with silicon(IV) oxide, an acidic impurity in the iron ore, to form slag. Write an equation for this reaction.

[2]

iii) Explain why the molten iron and the molten slag form two layers and why molten iron is the lower layer.

[1]

iv) Suggest why the molten iron does not react with the air.

[2]

Iron and steel rust. Iron is oxidised to hydrated iron(III) oxide, Fe₂O₃.2H₂O, which is rust.

i) Name the two substances which cause iron to rust.

[1]

ii) Explain why an aluminium article coated with aluminium oxide is protected from further corrosion but a steel article coated with rust continues to corrode.

[1]

Extended Only

There are two electrochemical methods of rust prevention.

i) The first method is sacrificial protection. Explain why the steel article does not rust.

[4]

ii) The second method is to make the steel article the cathode in a circuit for electrolysis. 

Mark on the diagram the direction of the electron flow.

[1]

iii) The steel girder does not rust because it is the cathode. Reduction takes place at the cathode. Give the equation for the reduction of hydrogen ions.

[2]