Extracting metals with carbon (reduction)
Most metals are found combined with other elements in ores — usually as oxides, sulfides or carbonates. Extraction is the process of obtaining the pure metal. The method depends on the metal's position in the reactivity series.
The big rule
- Metals below carbon (Zn, Fe, Sn, Pb, Cu) can be extracted by reduction with carbon.
- Metals above carbon (K, Na, Ca, Mg, Al) must be extracted by electrolysis of their molten compounds (see C4.11).
- A few unreactive metals (Au, sometimes Ag) are found native (uncombined) in the Earth.
How carbon reduction works
Carbon is more reactive than the metal, so it "steals" the oxygen from the metal oxide:
metal oxide + carbon → metal + carbon dioxide (or carbon monoxide)
The metal oxide is reduced (loses oxygen). The carbon is oxidised (gains oxygen).
Iron — the blast furnace
Iron(III) oxide reacts with carbon (or carbon monoxide produced by hot coke) in a blast furnace:
Fe₂O₃ + 3C → 2Fe + 3CO (or with CO: Fe₂O₃ + 3CO → 2Fe + 3CO₂)
The iron is reduced; the carbon is oxidised.
Copper from copper(II) oxide
A typical school example: 2CuO + C → 2Cu + CO₂
Black CuO turns to pinkish-brown Cu when heated with carbon powder.
Why aluminium can't be extracted with carbon
Aluminium is above carbon in the reactivity series, so carbon can't displace Al from Al₂O₃. Instead, electrolysis of molten aluminium oxide (mixed with cryolite to lower the melting point) is used (C4.11). Electrolysis is energy-expensive — that's why aluminium production is so power-hungry.
✦Worked example
A student heats 16 g of CuO with excess carbon. Calculate the maximum mass of copper produced.
2CuO + C → 2Cu + CO₂
- M_r CuO = 64 + 16 = 80, so moles CuO = 16/80 = 0.2.
- Mole ratio CuO : Cu = 1 : 1, so moles Cu = 0.2.
- Mass Cu = 0.2 × 63.5 ≈ 12.7 g.
⚠Common mistakes
- "Carbon extracts all metals" — only those below carbon in the reactivity series.
- Confusing oxidation/reduction. The metal oxide is reduced; carbon is oxidised. Easy to flip.
- Thinking aluminium ore is not abundant — it is (bauxite). The issue is energy, not availability.
- Forgetting bayan/native metals — gold and platinum are found uncombined.
Links
Builds on C4.1 (reactivity series). Sets up C4.11 (electrolytic extraction of Al), C10.4 (alternative methods like phytomining/bioleaching).
AI-generated · claude-opus-4-7 · v3-deep-chemistry