Alloys and Extraction of Metals

This guide covers the remaining subtopics of Topic 9, Metals — 9.2 Uses of metals, 9.3 Alloys and their properties and 9.6 Extraction of metals — for Cambridge IGCSE Chemistry 0620 and Cambridge O Level Chemistry 5070, 2026–2028 series. Properties and reactivity (9.1, 9.4, 9.5) are covered in Metal Properties and Reactivity.

Where this fits in 0620/5070

This half of Topic 9 is the applied side: given what a metal is like and how reactive it is (the other half of this topic), why is it used for a particular job, why do we alloy it rather than use it pure, and how do we actually get it out of the ground? Extraction in particular leans directly on the reactivity series and on redox as reduction — carbon reduces iron oxide, electrolysis reduces aluminium oxide — tying this topic back to both Metal Properties and Reactivity and Redox Reactions.

Syllabus coverage

CAMBRIDGE IGCSE CHEMISTRY 0620

Core

• Describing uses of metals in terms of their physical properties: aluminium in aircraft (low density), aluminium in overhead cables (low density, good conductivity), aluminium in food containers (corrosion resistance), copper in electrical wiring (conductivity, ductility) (9.2)
• Describing an alloy as a mixture of a metal with other elements — brass (copper + zinc), stainless steel (iron + chromium, nickel, carbon) (9.3)
• Stating that alloys are generally harder and stronger than the pure metals they’re made from, and more useful as a result (9.3)
• Describing uses of alloys in terms of their properties, e.g. stainless steel in cutlery for hardness and rust resistance (9.3)
• Identifying alloys from diagrams of their structure (9.3)
• Describing the ease of extracting a metal in terms of its position in the reactivity series (9.6)
• Describing the extraction of iron from hematite in the blast furnace (9.6)
• Stating that aluminium’s main ore is bauxite, extracted by electrolysis (9.6)

9.2 has no Extended-only content at all — every 9.2 outcome above is Core, for every 0620 candidate.

Supplement / Extended

• Explaining, in terms of structure, why alloys are harder and stronger than pure metals — different-sized atoms disrupt the regular layers, so they can no longer slide over each other (9.3)
• Stating the symbol equations for each step of extracting iron from hematite (9.6)
• Describing the extraction of aluminium from purified bauxite in detail, including the role of cryolite, why carbon anodes need regular replacement, and the electrode reactions (9.6)

CAMBRIDGE O LEVEL CHEMISTRY 5070

5070 has no Core/Extended split — every outcome above, Core and Supplement alike, is required for every O Level candidate.

Uses of metals

A metal’s uses follow directly from its physical properties (covered in Metal Properties and Reactivity), not from arbitrary tradition:

Metal	Use	Property that explains it
Aluminium	Aircraft manufacture	Low density
Aluminium	Overhead electrical cables	Low density + good electrical conductivity
Aluminium	Food containers	Resistance to corrosion
Copper	Electrical wiring	Good electrical conductivity + ductility

Notice the pattern examiners expect: every “use” answer should be paired with the specific property that makes it suitable — “aluminium is used in aircraft” alone earns no credit without “because of its low density.”

Alloys

An alloy is a mixture of a metal with one or more other elements, usually other metals or carbon. Two named examples:

• Brass — copper + zinc.
• Stainless steel — iron + chromium, nickel and carbon.

Why alloys are harder than pure metals. In a pure metal, atoms are all the same size, arranged in orderly layers that can slide over each other under stress — this is what makes pure metals relatively soft and malleable. Adding atoms of a different size (the alloying element) disrupts this regularity: the layers can no longer slide smoothly past one another, so more force is needed to deform the structure. This is why brass is harder than pure copper, and stainless steel is harder and more corrosion-resistant than pure iron.

Identifying alloys from structure diagrams. In a diagram of a pure metal, all the circles (atoms) are drawn the same size, arranged in regular, ordered rows. In a diagram of an alloy, you should see circles of at least two different sizes mixed together, with the regular layered arrangement visibly disrupted — that mismatch in atom size, drawn explicitly, is what marks a diagram as showing an alloy rather than a pure metal.

Uses of alloys follow the same property-then-use logic as pure metals: stainless steel is used for cutlery specifically because it combines hardness with resistance to rusting — a combination pure iron doesn’t offer.

Extraction of metals

How easily a metal can be extracted depends directly on its position in the reactivity series: the less reactive a metal, the more easily it’s obtained from its ore, because less energy is needed to reduce its compound back to the metal. Very unreactive metals like gold are sometimes even found uncombined (“native”) in the Earth’s crust.

Extracting iron: the blast furnace

Iron is extracted from its ore, hematite (iron(III) oxide), by reduction with carbon in a blast furnace:

1. Carbon (coke) burns, providing heat and producing carbon dioxide:
   C + O2 → CO2

2. Carbon dioxide is reduced to carbon monoxide by more coke:
   C + CO2 → 2CO

3. Carbon monoxide reduces iron(III) oxide to iron:
   Fe2O3 + 3CO → 2Fe + 3CO2

4. Limestone (calcium carbonate) thermally decomposes:
   CaCO3 → CaO + CO2

5. Calcium oxide reacts with silica (sand) impurities to form slag:
   CaO + SiO2 → CaSiO3

Steps 1–3 are the extraction itself — carbon, and then carbon monoxide, act as the reducing agent. Steps 4–5 remove the acidic silica impurity as molten slag, which floats on the molten iron and is drawn off separately.

Extracting aluminium: electrolysis

Aluminium is significantly more reactive than iron, so carbon reduction isn’t strong enough to extract it — instead, aluminium is extracted from purified bauxite (aluminium oxide) by electrolysis.

The aluminium oxide is dissolved in molten cryolite, which lowers its melting point enough to make electrolysis economically practical (pure aluminium oxide melts above 2000°C).

at the cathode (reduction): Al³⁺ + 3e⁻ → Al
at the anode (oxidation):   2O²⁻ → O2 + 4e⁻

The carbon anodes need regular replacement: the oxygen produced at the anode reacts with the hot carbon itself, burning it away as carbon dioxide.

Common mistakes

• Stating a use of a metal without the linking property. “Copper is used for wiring” gets no credit alone — the answer needs “…because of its good electrical conductivity and ductility.”
• Explaining alloy hardness by saying atoms are “mixed up” without mentioning size or layers. The expected explanation is specifically that different-sized atoms disrupt the regular layer structure, stopping the layers sliding over each other.
• Mixing up which reagent reduces which oxide in the blast furnace. Carbon monoxide (not carbon directly) reduces iron(III) oxide in the main reduction step — carbon’s first job is reducing CO₂ to CO.
• Forgetting why aluminium can’t be extracted by carbon reduction like iron. It’s not that nobody tried — aluminium is more reactive than carbon, so carbon cannot reduce aluminium oxide; electrolysis is needed instead.
• Assuming slag is a waste step with no purpose worth explaining. Slag formation removes silica impurities from the ore — know what it removes and why, not just that it happens.

Quick revision checklist

• Uses of aluminium and copper, each paired with the specific property that explains it
• What an alloy is, and the two named examples (brass, stainless steel)
• (0620 Extended, 5070 required) why alloys are harder than pure metals, explained structurally
• Extraction method linked to reactivity: carbon reduction for moderately reactive metals, electrolysis for the most reactive
• The five-step blast furnace sequence for extracting iron, in order
• (0620 Extended, 5070 required) symbol equations for each blast-furnace step
• Aluminium extraction by electrolysis: the role of cryolite, and why carbon anodes need replacing

Related resources

• Metal Properties and Reactivity — properties and the reactivity series behind these uses and extraction methods
• Redox Reactions — reduction, applied here to extracting iron and aluminium
• Electrolysis and Fuel Cells — the general principles of electrolysis that the aluminium extraction cell on this page applies
• Cambridge IGCSE Chemistry hub · Cambridge O Level Chemistry hub

Written against Cambridge IGCSE Chemistry 0620 and Cambridge O Level Chemistry 5070, 2026–2028 series. Always check the current syllabus for your examination year.