CBSE · Class 10 · Science · Metals and Non-metalsExplain the extraction process of metals from their ores based on their position in the activity series. Specifically detail: Extraction of metals low in the reactivity series (with suitable chemical equations). Differentiate between Roasting and Calcination with chemical equations for metals in the middle of the reactivity series.
Step-by-Step Solution
Extraction of Metals Based on Reactivity
\nMetals are extracted from their ores based on their reactivity order in the activity series:
1. Extraction of Metals Low in the Reactivity Series\nMetals low in the reactivity series are very unreactive. The oxides of these metals can be reduced to metals by heating alone.
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Example: Extraction of Mercury from Cinnabar ($HgS$):
- Step 1: Cinnabar ($HgS$) is first heated in air to convert it into mercuric oxide ($HgO$). $$2HgS(s) + 3O_2(g) \xrightarrow{\Delta} 2HgO(s) + 2SO_2(g)$$
- Step 2: Mercuric oxide is then reduced to mercury metal upon further heating. $$2HgO(s) \xrightarrow{\Delta} 2Hg(l) + O_2(g)$$
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Example: Extraction of Copper from Copper Pyrites/Glance ($Cu_2S$): $$2Cu_2S(s) + 3O_2(g) \xrightarrow{\Delta} 2Cu_2O(s) + 2SO_2(g)$$ $$2Cu_2O(s) + Cu_2S(s) \xrightarrow{\Delta} 6Cu(s) + SO_2(g)$$
2. Difference Between Roasting and Calcination
\nMetals in the middle of the reactivity series (like $Fe, Zn, Pb$) are usually present as sulphides or carbonates in nature. Before reduction, they are converted into metal oxides using Roasting or Calcination.
| Feature | Roasting (भर्जन) | Calcination (निस्तापन) |
|---|---|---|
| Definition | The process of heating sulfide ores strongly in the presence of excess air. | The process of heating carbonate ores strongly in limited air or absence of air. |
| Type of Ore | Used for Sulphide ores. | Used for Carbonate ores. |
| Gas Evolved | Sulphur dioxide ($SO_2$) gas is liberated. | Carbon dioxide ($CO_2$) gas is liberated. |
| Chemical Reaction Example | Zinc Sulphide ($ZnS$):<br>$2ZnS(s) + 3O_2(g) \xrightarrow{\Delta} 2ZnO(s) + 2SO_2(g)$ | Zinc Carbonate ($ZnCO_3$):<br>$ZnCO_3(s) \xrightarrow{\Delta} ZnO(s) + CO_2(g)$ |
| \nAfter obtaining the metal oxide ($ZnO$), it is reduced to metallic zinc using a suitable reducing agent such as carbon (coke): | ||
| $$ZnO(s) + C(s) \rightarrow Zn(s) + CO(g)$$ |
💡 Study Guide: This question tests core syllabus concepts from Metals and Non-metals. For formulas, key summaries, and mock exam reference guides, read the full Metals and Non-metals Revision Notes.