Attempt either option (A) or (B). Option (A):
Generated by claude-sonnet-4-6 · 2026-06-14 10:34 · grounding rag
Model Answer
(i)
(a) Carbonate ore → Calcination (heating in absence of air)
$$\text{ZnCO}_3 \xrightarrow{\Delta} \text{ZnO} + \text{CO}_2$$
(b) Sulphide ore → Roasting (heating in excess of air)
$$2\text{ZnS} + 3\text{O}_2 \xrightarrow{\Delta} 2\text{ZnO} + 2\text{SO}_2$$
(ii) Aluminium is used in the thermite reaction to join cracked railway tracks:
$$\text{Fe}_2\text{O}_3 + 2\text{Al} \rightarrow \text{Al}_2\text{O}_3 + 2\text{Fe} + \text{Heat}$$
The large amount of heat produced melts iron, which joins the tracks.
(iii) For electrolytic refining of copper:
- Anode → Impure copper (thick block)
- Cathode → Pure copper (thin strip)
- Electrolyte → Copper sulphate (CuSO₄) solution
Source: Metals and Non-metals, Sections on Extraction of Metals and Electrolytic Refining
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Explanation
- (i) is the key distinction: calcination = carbonate ores, roasting = sulphide ores. Examiners expect the correct term + equation.
- (ii) The thermite reaction equation must be balanced and written exactly; the mention of heat/joining is expected.
- (iii) Remember: anode = impure metal, cathode = pure metal — this is a frequently tested fact. The electrolyte (CuSO₄ solution) is often missed; include it.