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Give preparation of potassium dichromate and state its uses |
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Answer» Solution :Preparation: The yellow coloured sodium CHROMATE is obtained by FUSION of chromite ore `[FeCr_(2)O_(4)]` with sodium carbonate in free access of air `4FeCr_(2)O_(4) + 8Na_(2)CO_(3) + 7O_(2) rarr 8Na_(2) CrO_(4) + 2Fe_(2)O_(3) + 8CO_(2)` The yellowcoloured solution of sodium chromate is filtered and acidified with sulphuric acid to GIVE a solution from which orange sodium dichromate `Na_(2)Cr_(2)O_(7). 2H_(2)O` ca be crystallized out `2Na_(2)CrO_(4) + 2H^(+) rarr Na_(2)Cr_(2)O_(7) + 2Na^(+) + H_(2)O` Sodium dichromate is more soluble than potassium dichromate. The latter is therefore PREPARED by treating the solution of sodium dichromate with potassium chloride. `Na_(2)Cr_(2)O_(7) + 2KCl rarr K_(2)Cr_(2)O_(7) + 2NaCl` |
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