InterviewSolution
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InterviewSolution
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An aqueous solution of metal chloride `MCI_(2)(0.05M)` is saturated with `H_(2)S (0.1M)`. The minimum `pH` at which metal sulphide will be precipiated is `[K_(sp)MS = 5 xx 10^(-21),K_(1)(H_(2)S) = 10^(-7),K_(2)(H_(2)S) = 10^(-14)`.A. `3.25`B. `2.50`C. `1.50`D. `1.25` |
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Answer» Correct Answer - C `K_(sp) MS = [M^(2+)] [S^(2-)]` `5 xx 10^(-21) = (0.05) [S^(2-)]` For precipitation `Q_(sp) = K_(sp)` `:. [S^(2-)] = (5 xx 10^(-21))/(5xx10^(-2)) = 10^(-19)` For `H_(2)S:` `H_(2)S hArr H^(o+) +HS^(Theta) (K_(1))` `HS^(Theta) hArr H^(o+) +S^(2-) (K_(2))` `K_(1)xx K_(2) =([H^(o+)]^(2)[S^(2-)])/(H_(2)S)` `10^(-7) xx 10^(-14) = ([H^(o+)]^(2)[10^(-19)])/(0.1)` `[H^(o+)]^(2) = 10^(-3), rArr` [Taking negative logaritham both sides] `-2 log [H^(o+)] = 3` `pH = (3)/(2) = 1.5` |
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