Extraction of MetalsOxford AQA IGCSE Chemistry: Revision notes

Most metals are found in the Earth's crust combined with other elements, as compounds (usually oxides or other ores), because reactive metals readily bond with other elements. The method used to extract a metal from its compound depends on how reactive the metal is:

• Very unreactive metals (e.g. gold) are found as the metal itself — no chemical extraction needed
• Metals less reactive than carbon can be extracted by reduction with carbon
• Metals more reactive than carbon must be extracted by electrolysis

Metals less reactive than carbon (such as iron) are extracted by heating their oxide with carbon. The carbon reduces the metal oxide, removing the oxygen:

metal oxide + carbon → metal + carbon dioxide

This works because carbon is more reactive than the metal, so it takes the oxygen from the metal oxide, leaving the pure metal behind.

Iron oxide is reduced in a blast furnace using three raw materials: iron ore (haematite), coke (carbon) and limestone, along with hot air.

The key reactions:

1. Coke burns in the hot air blast: C + O₂ → CO₂
2. Carbon dioxide reacts with more coke to form carbon monoxide: CO₂ + C → 2CO
3. Carbon monoxide reduces the iron oxide: Fe₂O₃ + 3CO → 2Fe + 3CO₂

Molten iron collects at the bottom of the furnace and is tapped off.

Metals such as aluminium, which are more reactive than carbon, cannot be reduced by carbon — carbon cannot remove oxygen from their oxides. Instead, these metals must be extracted by electrolysis of their molten compounds.

Electrolysis requires large amounts of electrical energy to melt the compound and drive the reaction, which makes this extraction method much more expensive than reduction with carbon.