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Explain isolation of metals from concentrated ore. |
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Answer» Solution :The PROCESS of ISOLATION of metals from concentrated ore involves two steps: (i) Conversion to oxide and (ii) Reduction of the oxide to metal Step-1 : Conversion to oxide : (i) Calcination : Calcination involves heating. It removes the volatile MATTER which escapes leaving behind the metal oxide : `Fe_2O_(3) cdot xH_2O_((s)) overset(Delta)(rarr) Fe_(2)O_(3(s)) + xH_2O_((g))` `ZnCO_(3(s)) overset(Delta)(rarr)ZnO_((s)) + CO_(2(g))` `CaCO_(3) cdot MgCO_(3(s)) overset(Delta)(rarr) CaO_((s)) + MgO_((s)) + 2CO_(2(g))` . (ii) Roasting: In roasting, the ore is heated in a regular supply of air in a furnace at a temperature below the MELTING point of the metal. Some of the reactions involving sulphide ores are : `2Zn_((s)) + 3O_(2(g)) to 2ZnO_((g)) + 2SO_(2(g))` `2PbS_((s)) + 3O_(2(g)) to 2PbO_((s)) + 2SO_(2(g)) ` `2Cu_(2)S_((s)) + 3O_(2(g)) to 2Cu_(2)O_((s)) + 2SO_(2(g))`. The sulphide ores of copper are heated in reverberatory furnace. If ore contains iron, it is mixed with silica before heating. Iron oxide "slags off" as iron silicate and copper is produced in the form of copper matte which contains `Cu_2S and FeS.`  The `SO_2` produced is utilised in manufacturing of `H_2SO_4`. The sulphide ores are usually converted to oxide ores before reduction because reduction of oxide ore is easier. Step-2 : Reduction of oxide to the metal : Reduction of the metal oxide usually involves heating it with a reducing agent such as carbon or carbon monoxide or even another metal. The reducing agent (e.g., carbon) combines with the oxygen of the metal oxide. `M_xO_y + yC to xM + yCO` Some metal oxides get reduced easily while others are very difficult to be reduced (reduction means electron gain by the metal ion). In any case, heating is required. |
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