Metals and their extraction

ZIMSEC O Level · Chemistry · Form 4

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Reactivity series

K, Na, Ca, Mg, Al, (C), Zn, Fe, Pb, (H), Cu, Ag, Au. More reactive metals displace less reactive ones from solutions of their salts, e.g. Zn + CuSO₄ → ZnSO₄ + Cu.

Extraction

The method depends on reactivity:

Above carbon: electrolysis of the molten ore (aluminium, sodium).
Below carbon: reduction with carbon or carbon monoxide (iron, zinc, lead).
Very unreactive: found as the metal (gold).

The blast furnace (iron)

Raw materials: iron ore (haematite, Fe₂O₃), coke and limestone.

C + O₂ → CO₂; then CO₂ + C → 2CO
Fe₂O₃ + 3CO → 2Fe + 3CO₂
Limestone decomposes to CaO, which reacts with sand (SiO₂) to form slag (CaSiO₃), removing impurities.

Alloys and uses

Steel (iron with carbon) is stronger; stainless steel resists rusting; brass (copper and zinc). Aluminium is light and resists corrosion (oxide layer) – used for aircraft and pots. Copper conducts well – used for wiring.

Rusting

Iron needs water and oxygen to rust. Prevention: painting, greasing, galvanising, sacrificial protection with a more reactive metal (zinc or magnesium).

Exam tip: In sacrificial protection, the more reactive metal corrodes instead of the iron.

Check yourself

Why is aluminium extracted by electrolysis, not by carbon?
State the role of limestone in the blast furnace.
Explain why galvanised iron does not rust even when scratched.

Show answers

Aluminium is more reactive than carbon, so carbon cannot reduce its oxide.
It removes impurities (sand) as slag.
Zinc is more reactive and corrodes in preference to iron (sacrificial protection).

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