AQA GCSE Chemistry Foundation (8462), Foundation tier · Chemical changes › Reactivity of metals
Practise Extraction of metals and reduction. 6 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.
Key facts
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
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
diagram
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.
Find the metal, then look at which side of carbon it is on.
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.
How to answer each type of question
Explain the choice of extraction method
2 marksGrade 5
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 answerHide 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)
Don’t lose marks
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.
More tips
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.
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.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
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.
Grade 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.
Grade 5
Write equations for reduction with carbonFor example, 2ZnO + C → 2Zn + CO2.
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
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)