Exam Frequency Analysis
Past paper frequency (2018 to 2024)
This topic accounts for approximately 6% of your exam marks.
stable
Low
Stable6%
Blast furnace chemistry and electrolytic extraction of aluminium regularly examined.
Choosing an extraction method from the reactivity series
- Metals above carbon in the reactivity series (K, Na, Li, Ca, Mg, Al) are too reactive to be reduced by carbon
- They must be extracted by electrolysis of their molten compound
- Metals below carbon but above the unreactive group (Zn, Fe, Sn, Pb, Cu) can be reduced by heating their oxide with carbon (or carbon monoxide)
- Metals below hydrogen (Cu, Ag, Au) are unreactive and the least reactive of these are simply mined as the free element
| Metal | Position relative to carbon | Extraction method |
|---|---|---|
| K, Na, Ca, Mg, Al | Above carbon | Electrolysis of the molten compound |
| Zn, Fe, Sn, Pb | Below carbon | Reduction by heating with carbon or carbon monoxide |
| Cu | Below carbon | Reduction by heating with carbon (or roasting copper sulfide) |
| Ag, Au, Pt | Native (unreactive) |
Exam tip
Explaining which extraction method to use, and why
What comes up: a 2-mark question asking you to explain, using the reactivity series, why a particular method (carbon reduction or electrolysis) is suitable for extracting a named metal.
Write (two marks): (1) name the correct method (for iron: extraction by carbon/carbon monoxide; for sodium or aluminium: electrolysis); (2) justify it using position in the reactivity series — for iron, carbon is above iron in the reactivity series / carbon is more reactive than iron, so it can remove oxygen from iron(III) oxide; for sodium, sodium is above carbon in the reactivity series so carbon cannot reduce its compound.
Watch out: if the question specifies extraction using carbon versus electrolysis, naming the wrong method in M1 scores zero for the whole answer. State the method first, then give the reactivity reasoning.
Extraction of iron in the blast furnace
- Iron is extracted from haematite using a blast furnace — a continuous, high-temperature reactor charged at the top and tapped at the bottom
- Three raw materials are loaded in:
- Iron (haematite, Fe2O3) — the source of iron
- (an impure form of carbon) — the reducing agent and the source of heat
- (calcium carbonate, CaCO3) — to remove acidic impurities from the ore
- Hot air is blasted in near the bottom
The chemistry inside the furnace
- Combustion zone (hottest, near the air blast) — the coke ignites in the incoming blast of preheated air, supplying the heat that drives the rest of the furnace
Exam tip
State why aluminium cannot be extracted by heating its oxide with carbon
What comes up: a 1-mark question asking why reduction by carbon is not suitable for aluminium.
Write: aluminium is more reactive than carbon, so carbon cannot remove oxygen from aluminium oxide. Equivalently: aluminium is above carbon in the reactivity series (accept either form).
Watch out: the mark scheme accepts the reverse argument ("carbon is less reactive than aluminium") — so phrase it whichever way feels natural, but you must make the comparison explicit. Simply saying "aluminium is too reactive" without comparing to carbon does not clearly answer the question.