S5 Chemistry: Metal Extraction (Paper 4: Misconception Drill)

2026-11-12

Ten items on the commonest misconceptions: the direction of reactivity, what carbon can reduce, the blast furnace product, the roles of limestone and cryolite, and the anode reaction, with answers.

Direct answers　Answers in order: more reactive means harder, no it needs electrolysis, no it gives pig iron, no it forms slag, no it is a solvent, oxidation, 27.0 g, 289 500 C, 89.6 g, iron is reduced by carbon monoxide.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	20
Difficulty mix	Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1
Chapter	Chapter: S5 Chemistry: Metal Extraction
Level	S5

02　Questions (10 items)

FoundationWhat is wrong with the claim that the more reactive a metal the easier it is to extract?
FoundationCan carbon reduce aluminium oxide?
FoundationIs the product of the blast furnace steel?
IntermediateIs the limestone in the blast furnace a source of carbon?
IntermediateIs cryolite a catalyst?
IntermediateIs oxidation or reduction taking place at the anode in aluminium electrolysis?
ChallengeWhat mass of aluminium can be obtained in theory from 51.0 g of aluminium oxide, Al2O3 = 102 and Al = 27?
ChallengeFrom the previous question, what charge is needed in theory, with one mole of electrons equal to 96 500 C?
ChallengeWhat mass of iron is obtained from 160 g of iron(III) oxide at 80.0 percent yield?
Error redoA student says iron is extracted by electrolysis. What is wrong?

03　Answers and one-line notes

#	Answer	One-line note
1	It is the opposite: compounds of reactive metals are more stable and therefore harder to break down.	From potassium down to gold the difficulty falls, so potassium needs electrolysis while gold occurs native.
2	No, aluminium is more reactive than carbon and electrolysis is required.	Carbon reduces only oxides of metals below it, and the aluminium oxygen bond is far too strong.
3	No, the blast furnace gives pig iron with about four percent carbon; steel needs a further refining step.	Pig iron is hard and brittle, and only after excess carbon is oxidised away does it become steel.
4	No, the limestone forms slag and removes silica impurities.	Coke supplies the carbon; limestone decomposes to calcium oxide, which combines with silica to give calcium silicate slag.
5	No, it is a solvent that dissolves the oxide and lowers the melting point.	A catalyst is not consumed and does not shift the position of equilibrium; cryolite merely provides a molten medium so the cell runs cooler.
6	Oxidation: oxide ions discharge to oxygen, which then reacts with the carbon to form carbon dioxide.	Reduction happens at the cathode; the anode is always where oxidation occurs, a fixed rule for electrolytic cells.
7	27.0 g	51.0 g is 0.500 mol and each mole yields two moles of aluminium, giving 1.00 mol or 27.0 g.
8	289 500 C	Making 1.00 mol of aluminium needs 3.00 mol of electrons, and 3 times 96 500 is 289 500 C.
9	89.6 g	The theoretical mass is 112 g and multiplying by 0.800 gives 89.6 g to three significant figures.
10	Wrong. Iron lies below carbon and is extracted by reduction with carbon monoxide, so no electrolysis is needed.	Iron compounds are less stable than those of potassium, sodium and aluminium, so carbon suffices and the blast furnace replaces the cell.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

Turn every wrong item today into one sentence: I thought this, but actually that.Tutor Registration →

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