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In qualitative analysis, cations of group II as well as group IV precipitated in the form of sulphides. Due to low value of Ksp of group II sulphides, group reagent is H_(2)S in presence of dil. HCl and due to high value of Ksp of group IV sulphides, group reagent is H_(2)S in presence of NH_(4)OH and NH_(4)Cl. In 0.1M H_(2)S solution, Sn^(2+), Cd^(2+) and Ni^(2+) ions are present in equimolar concentration (0.1M). Given : Ka_(1)(H_(2)S) = 10^(-7), Ka_(2)(H_(2)S) = 10^(-14), K_(sp)(SnS) = 8 xx 10^(-29) , K_(sp) (CdS) = 10^(-28), K_(sp)(NiS) = 3 xx 10^(-21) At what pH precipitate of NiS will form |
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Answer» `12.76` `{:(H_(2)ShArrH^(+)+HS^(-1),k_(a_(1))=10^(-7)),(HS^(-1)hArrH^(+)+S^(-2),k_(a_(2))=10^(-14)):}` `k_(a_(2)) = ([H^(+)][S^(2)])/([HS^(-1)])` `k_(a_(1)).k_(a_(2)) = 10^(-21)([H^(+)]^(2)[3XX10^(-20)])/([0.1])` `[H^(+)] =sqrt((1)/(300)):.pH = 1.2388` |
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