Explain how a metal of medium reactivity, such as zinc, is extracted from its sulphide and carbonate ores, and how the metal is then refined.

1. 1 · Open in one line. Metals in the middle of the reactivity series occur as sulphides or carbonates, and are first changed into oxides.
2. 2 · Roasting. The sulphide ore is heated in excess air: 2ZnS(s) + 3O₂(g) → 2ZnO(s) + 2SO₂(g).
3. 3 · Calcination. The carbonate ore is heated in limited air: ZnCO₃(s) → ZnO(s) + CO₂(g).
4. 4 · Reduction. The oxide is heated with carbon: ZnO(s) + C(s) → Zn(s) + CO(g).
5. 5 · Refine, with a diagram. Refine by electrolysis: impure metal as the anode, a pure strip as the cathode, and a salt solution of the metal as the electrolyte. Draw and label the anode, cathode, electrolyte and anode mud.
6. 6 · Link to real life. Zinc is used to galvanise iron sheets for roofs and buckets.
7. 7 · Close in one line. So roasting or calcination, then reduction, then refining gives the pure metal.

Scoring tip: Write the air condition for each step: excess air for roasting, limited air for calcination. This is the mark most often lost.