Science (086) — AI-generated practice question

(i) Carbon can only reduce metal oxides to their respective metals. It cannot directly reduce sulphides or carbonates efficiently. Therefore, sulphide and carbonate ores must first be converted to metal oxides before reduction with carbon.

(ii)
(a) Sulphide ores are converted to oxides by roasting — heating strongly in the presence of excess air.
Example: $2\text{ZnS(s)} + 3\text{O}_2\text{(g)} \xrightarrow{\Delta} 2\text{ZnO(s)} + 2\text{SO}_2\text{(g)}$

(b) Carbonate ores are converted to oxides by calcination — heating strongly in limited air.
Example: $\text{ZnCO}_3\text{(s)} \xrightarrow{\Delta} \text{ZnO(s)} + \text{CO}_2\text{(g)}$

Source: Chapter 3, Section 3.4.4

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• Part (i) is worth ~1 mark — one clear reason is enough.
• Parts (ii)(a) and (ii)(b) are worth ~1 mark each — name the process AND give the equation; examiners expect both.
• Key terms to spell correctly: roasting (excess air) vs calcination (limited air) — mixing these up is a common error.