AQA GCSE Combined Science (8464), Higher tier · Chemistry › Chemical changes › Reactivity of metals
Practise Extraction of metals and reduction. 12 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Where metals come from, and how metals less reactive than carbon are extracted by heating their oxides with carbon (reduction). Questions often give information about an unfamiliar extraction and ask you to explain or evaluate it using the reactivity series.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Explain why gold is found as the metalGold is so unreactive that it is found in the Earth as the metal itself, not as a compound.
4
State which metals carbon can extractMetals below carbon in the reactivity series, such as zinc, iron and copper, can be extracted by heating their oxides with carbon.
5
Write equations for reduction with carbonFor example, 2ZnO + C → 2Zn + CO2.
6
Identify what is oxidised and reducedThe metal oxide loses oxygen so it is reduced; carbon gains oxygen so it is oxidised.
7
Evaluate an unfamiliar extraction methodUse the information given and the reactivity series to judge a method on energy, cost, raw materials and waste.
Notes
Where metals are found
Very unreactive metals such as gold are found in the Earth as the metal itself (uncombined).
Most metals are found as compounds, often oxides, in rocks. A rock that contains enough of a metal compound to make extraction worthwhile is called an ore.
Chemical reactions are needed to extract a metal from its compound.
Reduction with carbon
Metals less reactive than carbon can be extracted by heating their oxides with carbon.
Carbon removes the oxygen from the metal oxide. The metal oxide is reduced (loses oxygen) and the carbon is oxidised (gains oxygen).
Carbon is used because it is cheap and it is more reactive than these metals.
Metals more reactive than carbon
Metals more reactive than carbon (potassium, sodium, lithium, calcium, magnesium and aluminium) cannot be extracted by heating with carbon. They are extracted by electrolysis of their molten compounds.
Electrolysis needs a lot of energy, so it is more expensive than reduction with carbon.
Rule: find the metal in the reactivity series. Below carbon → reduce with carbon. Above carbon → electrolysis.
Evaluating an extraction process
You may be given information about a process you have not met. You do not need to learn the details of any industrial process.
Use the reactivity series to explain the choice of reactant, e.g. scrap iron can be added to copper sulfate solution to obtain copper, because iron is more reactive and displaces it.
Compare methods using the data given: energy needed, cost of raw materials, how much metal is produced, waste products and effects on the environment (e.g. carbon dioxide released). End with a conclusion. grade 7+
Cheatsheet
Ore = rock containing enough metal compound to make extraction worthwhile
Gold is found as the uncombined metal
Less reactive than carbon → extract by heating the oxide with carbon
More reactive than carbon → extract by electrolysis
Reduction = loss of oxygen; oxidation = gain of oxygen
2ZnO + C → 2Zn + CO2
2CuO + C → 2Cu + CO2
2Fe2O3 + 3C → 4Fe + 3CO2
How to answer each type of question
Explain the choice of extraction method
2 marks5
Find the metal and carbon in the reactivity series.
Below carbon: carbon is more reactive, so it can remove the oxygen from (reduce) the metal oxide.
Above carbon: carbon cannot reduce the oxide, so electrolysis is needed.
Example. Tin is extracted by heating tin oxide with carbon. Magnesium cannot be extracted in this way. Explain why.
Show the model answer
Tin is less reactive than carbon, so carbon can remove the oxygen from / reduce tin oxide (1) Magnesium is more reactive than carbon, so carbon cannot reduce magnesium oxide (1)
Balance the equation and identify what is oxidised
3 marks6
Balance one element at a time, then count atoms on both sides.
The substance that gains oxygen is oxidised; the one that loses oxygen is reduced.
Give the reason in terms of oxygen.
Example. Copper can be extracted by heating copper(II) oxide with carbon. (a) Balance the equation: ....CuO + C → ....Cu + CO2 (b) Which substance is oxidised? Give a reason for your answer.
Show the model answer
(a) 2CuO + C → 2Cu + CO2 (1) (b) Carbon (1) because it gains oxygen (to form carbon dioxide) (1)
Evaluate an extraction process from given information
4 to 6 marks7
Pick out the facts in the information: temperature, energy, cost of reactants, speed, waste.
Turn each fact into an advantage or a disadvantage and say why.
Use the reactivity series to explain why the reaction works.
Finish with a conclusion if the question asks for a judgement.
Example. Titanium cannot be extracted by heating its oxide with carbon. In one process, titanium chloride is heated with sodium at a high temperature in an atmosphere of argon: TiCl4 + 4Na → Ti + 4NaCl Sodium is extracted by electrolysis of molten sodium chloride. The process is done in batches. Evaluate this method of producing titanium. [4 marks]
Show the model answer
Any four from: sodium is more reactive than titanium, so it displaces titanium from titanium chloride (1) heating to a high temperature needs a lot of energy, which is expensive (1) sodium is expensive because electrolysis uses a lot of electrical energy (1) argon (an unreactive gas) is needed to stop the hot metals reacting with oxygen in the air, which adds to the cost (1) a batch process is slow, so less titanium is made in a given time (1) conclusion: the method works, but it makes titanium an expensive metal (1)
Shortcuts and memory tricks
Draw a line at carbon in the reactivity series: above the line → electrolysis, below the line → heat with carbon.
A metal oxide is 'reduced' down to the bare metal: it loses oxygen.
In a carbon reduction equation, carbon always ends up as carbon dioxide (or carbon monoxide) on the right.
Where marks are lost
Saying carbon is used because it is 'more reactive' without saying it removes oxygen from the metal oxide.
Saying the metal is oxidised during extraction: the metal oxide is reduced.
Thinking carbon can extract aluminium or magnesium: both are more reactive than carbon.
Writing only general points in an evaluation instead of using the information given.
Exam technique
In 'evaluate' questions, give advantages and disadvantages and finish with a conclusion supported by the information.
Use the phrase 'more reactive than carbon' or 'less reactive than carbon' whenever you explain a method.
You do not need to learn industrial details (such as the blast furnace): the question gives you what you need.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Complete the sentence. Reduction is the .................... of oxygen.
loss
Tin is extracted by heating tin(IV) oxide, SnO2, with carbon. The products are tin and carbon dioxide. Write a balanced symbol equation for this reaction.
SnO2 + C → Sn + CO2
Tungsten is a metal used to make welding electrodes. Tungsten is less reactive than carbon. However, if tungsten oxide is heated with carbon, some of the tungsten produced reacts with the carbon to form tungsten carbide. Instead, tungsten is extracted by heating tungsten oxide with hydrogen at a high temperature: WO3 + 3H2 → W + 3H2O Name the substance that is oxidised.
hydrogen
A student heats a mixture of black copper(II) oxide powder and carbon powder strongly in a boiling tube. The tube is connected to a second tube containing limewater. Write a word equation for the reaction in the first tube.
copper oxide + carbon → copper + carbon dioxide
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Most metals are found in the Earth's crust as compounds. Chemical reactions are needed to extract the metals.
(a) Gold is found in the Earth as the metal itself. Explain why.[1]
(b) Which metal can be extracted by heating its oxide with carbon? Tick (✓) one box.[1]
Aluminium
Iron
Magnesium
Sodium
(c) Complete the sentence. Reduction is the .................... of oxygen.[1]
(d) Zinc is extracted by heating zinc oxide with carbon: zinc oxide + carbon → zinc + carbon monoxide Which substance is reduced in this reaction?[1]
Show the answer and mark scheme
(a)
gold is very unreactive (so it does not form compounds)
(b)Answer: Iron
(c)Answer: loss
loss / removal
(d)Answer: zinc oxide
zinc oxide
Question 2Medium6 marks
Part of the reactivity series is shown below, with the most reactive element first. potassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iron, tin, copper
(a) Name two metals in the list that can be extracted by heating their oxides with carbon.[2]
(b) Explain why aluminium cannot be extracted by heating aluminium oxide with carbon.[1]
(c) Tin is extracted by heating tin(IV) oxide, SnO2, with carbon. The products are tin and carbon dioxide. Write a balanced symbol equation for this reaction.[1]
(d) Identify the substance that is oxidised in the extraction of tin. Give a reason for your answer.[2]
Show the answer and mark scheme
(a)
one from zinc / iron / tin / copper
a second, different metal from zinc / iron / tin / copper
(b)
aluminium is more reactive than carbon (so carbon cannot remove oxygen from aluminium oxide)
(c)Answer: SnO2 + C → Sn + CO2
SnO2 + C → Sn + CO2
(d)
carbon
it gains oxygen (to form carbon dioxide)
Question 3Hard6 marks
Tungsten is a metal used to make welding electrodes. Tungsten is less reactive than carbon. However, if tungsten oxide is heated with carbon, some of the tungsten produced reacts with the carbon to form tungsten carbide. Instead, tungsten is extracted by heating tungsten oxide with hydrogen at a high temperature: WO3 + 3H2 → W + 3H2O
(a) Explain why this reaction is a reduction of tungsten oxide.[1]
(b) Name the substance that is oxidised.[1]
(c) Suggest why hydrogen, rather than carbon, is used to extract tungsten.[1]
(d) Suggest one disadvantage of using hydrogen to extract tungsten.[1]
(e) Calculate the maximum mass of tungsten that can be extracted from 46.4 kg of tungsten oxide. Relative atomic masses (Ar): O = 16, W = 184[2]
Show the answer and mark scheme
(a)
tungsten oxide loses oxygen
(b)Answer: hydrogen
hydrogen
(c)
carbon would react with the tungsten / form tungsten carbide, so the tungsten would be impure
(d)
hydrogen is flammable / explosive (with air)
hydrogen has to be made first, which uses energy / is expensive
a high temperature is needed, so energy costs are high