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Group I filtrate is made moderately acidic before proceeding to group II. Expain. |
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Answer» Solution :precipitation of the sulphide can occur only when the ionic product `[M^(2+)][S^(2)]` exceeds the solubility product of the sulphides. MS In the presenc of acid, the ionisation of `H_(2)S` is suppressed due to the INCREASED concentration of `H^(o+)`. As a result, there are only few `S^(2-)` ions in solution which are enough to precipitate only group II cations as sulphides e.g., `Cus,PbS` etc. But for the precipitation of CDS, the concentration of `S^(2-)` is not enough. HENCE the concentration of `(H^(o+))` should be further decreased by diluting the solution so that the `H_(2)S` is ionised extensively As a result `S^(2-)` ions are made available in sufficient quantity which can precipitate thhe `Cd^(2+)` ions i.e., ionic product `[Cd^(2+)][S^(2-)]` exceeds solubility product of CdS. |
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