Reactivity series and metal extraction

The reactivity series ranks metals by how readily they lose electrons (form positive ions). It controls how the metal corrodes, displaces other metals, and — critically — how it is extracted from its ore.

The reactivity series (most → least reactive)

K, Na, Li, Ca, Mg, Al, C, Zn, Fe, Sn, Pb, (H), Cu, Ag, Au.

Carbon and hydrogen are included as reference points: any metal less reactive than carbon can be reduced from its oxide by heating with carbon (e.g. iron in the blast furnace). Metals more reactive than carbon must be extracted by electrolysis.

Displacement reactions

A more reactive metal displaces a less reactive metal from its salt solution. Mg(s) + CuSO₄(aq) → MgSO₄(aq) + Cu(s). Blue solution fades to colourless; brown copper deposits.

Extracting iron — blast furnace (reduction by carbon)

Raw materials: iron ore (haematite, Fe₂O₃), coke C, limestone (CaCO₃), hot air. Key equation: Fe₂O₃ + 3CO → 2Fe + 3CO₂. Carbon monoxide reduces iron(III) oxide; iron is more easily reduced than aluminium because it sits below carbon in the reactivity series.

Extracting aluminium — electrolysis

Aluminium oxide is dissolved in molten cryolite (lowers the operating temperature from ~2050 °C to ~950 °C and saves energy).

• Cathode (negative): Al³⁺ + 3e⁻ → Al (reduction).
• Anode (positive): 2O²⁻ → O₂ + 4e⁻ (oxidation). Carbon anodes burn away in the hot oxygen and must be replaced.

OILRIG

Oxidation Is Loss (of electrons), Reduction Is Gain. Apply this to half-equations.

CCEA tip

Always check: does the question want a word equation, a balanced symbol equation, or an ionic half-equation? Each requires a different style of working — read the verb.