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Is it necessary to acidify a solution before group II cations are precipitated with H_(2)S? |
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Answer» Solution :Yes, because for the precipitation of cations of group II only small CONCENTRATION of SULPHIDE ions `(S^(2-))` is required this condition is ACHIEVED by passing `H_(2)S` gas in a solution acidified with `HCL` (dil.) due to common ion effect concentration of `S^(2-)` ions decreases as presence of hydrochloric acid suppresses the ionisation of `H_(2)S` resulting only in the precipitation of sulphides of group II metals. Other metal sulphides remain in solution as they required higher concentration of `S^(2-)` ions for their precipitation. |
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