2.5.2Inorganic Chemistry

Extracting Metals — Edexcel International GCSE Science Double Award 4SD0 - Chemistry Revision Notes & Topical Questions

5 min read 5 parts Lesson 22 of 52

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Part 1 of 5Choosing an Extraction Method

Reactivity controls how easily a metal can be separated from its compound, so it sets the method used.

Above carbon

Very reactive metals such as aluminium, magnesium, calcium, sodium, lithium and potassium cannot be reduced by carbon and must be extracted by electrolysis of molten compounds.

Below carbon

Zinc, iron and copper are less reactive than carbon, so their oxides can be reduced by heating with carbon or carbon monoxide.

Unreactive metals

Gold and silver are so stable that they are often found as the uncombined element and need no chemical extraction.

Metal group	Method	Reason
Potassium to aluminium	Electrolysis	Too reactive to be reduced by carbon
Zinc, iron, copper	Reduction with carbon	Carbon is more reactive than these metals
Gold, silver	Found as the element	Very unreactive

Iron is produced continuously from hematite, coke and limestone in three zones.

Coke burns in hot air in the lower part of the furnace, giving carbon dioxide and releasing heat: C(s) + O₂(g) → CO₂(g).

At high temperature the carbon dioxide reacts with more coke to form carbon monoxide: CO₂(g) + C(s) → 2CO(g).

Carbon monoxide reduces iron(III) oxide in the ore to molten iron: Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g).

Limestone decomposes to calcium oxide, which reacts with silicon dioxide impurities to form molten slag that floats on the iron.

Bauxite is purified to aluminium oxide, which is dissolved in molten cryolite before electrolysis.

Aluminium by Electrolysis

Cryolite

Dissolving aluminium oxide in molten cryolite lowers the melting point, saving a large amount of energy.

Cathode

Aluminium ions gain electronsAl³⁺ + 3e⁻ → Al, and molten aluminium collects at the bottom of the cell.

Anode

Oxide ions lose electrons2O²⁻ → O₂ + 4e⁻, and the oxygen reacts with the graphite anode to form carbon dioxide.

Cost

Large amounts of electricity are needed and the graphite anodes wear away, so they must be replaced regularly.

Question

Calculate the maximum mass of iron that can be obtained from 800 kg of iron(III) oxide, Fe₂O₃, assuming a 100% yield.
(Ar: Fe = 56, O = 16)

Mr of Fe₂O₃ = (2 × 56) + (3 × 16) = 112 + 48 = 160.
Mass of iron in one mole of Fe₂O₃ = 2 × 56 = 112, so the fraction of the compound that is iron = 112 ÷ 160 = 0.70.
Mass of iron = 800 kg × 0.70 = 560 kg.

Answer 560 kg of iron (maximum, assuming a 100% yield).

Ore A rock containing enough of a metal compound to make extraction worthwhile.
Reduction A reaction in which a substance gains electrons or loses oxygen.
Electrolysis Decomposition of a molten ionic compound by passing electricity through it.
Cryolite A substance used to dissolve aluminium oxide so that it melts at a lower temperature.
Slag A waste material formed when limestone removes impurities from iron ore.

Saying carbon reduces aluminium oxide;
- aluminium is above carbon in the reactivity series, so electrolysis is needed.
Stating that limestone is a reducing agent; its job is to remove acidic silicon dioxide impurities as slag.
Writing that molten iron is removed as a gas, when it is tapped off from the bottom of the furnace as a liquid.
Forgetting that the anode carbon is used up, so it must be replaced regularly during aluminium extraction.

Last updated: 28 October 2026