With the help of suitable chemical equations, list the two main differences between roasting and calcination. How is metal reduced from the product obtained after roasting/calcination of the ore ? Write the chemical equation for the reaction involved.
Generated by claude-sonnet-4-6 · 2026-06-15 06:48 · grounding rag
Model Answer
Differences between Roasting and Calcination:
| | Roasting | Calcination |
|---|---|---|
| 1. | Ore is heated in excess of air/oxygen | Ore is heated in limited/absence of air |
| 2. | Applied to sulphide ores | Applied to carbonate/hydroxide ores |
Chemical equations:
Roasting: $2\text{ZnS} + 3\text{O}_2 \rightarrow 2\text{ZnO} + 2\text{SO}_2$
Calcination: $\text{ZnCO}_3 \xrightarrow{\Delta} \text{ZnO} + \text{CO}_2$
Reduction of metal from oxide:
The metal oxide obtained is reduced using a suitable reducing agent like carbon (coke):
$$2\text{ZnO} + \text{C} \rightarrow 2\text{Zn} + \text{CO}_2$$
Source: Metals and Non-metals, Section 3.3 (Extraction of Metals)
---
Explanation
- Examiners expect both differences clearly stated — the key distinguishing points are (i) presence/absence of air and (ii) type of ore.
- One equation for each process is sufficient; ZnS/ZnCO₃ are standard textbook examples.
- For reduction, carbon reduction is the most common expected example. Some questions also accept thermite/aluminium reduction for highly reactive metal oxides, but carbon reduction suffices here.
- Do not mix up roasting (sulphides → oxides) with calcination (carbonates → oxides).