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What is maximum pH required to prevent the precipitation of ZnS in a solution that is 0.01 M `ZnCl_(2)` and saturated with 0.10M `H_(2)S`? [Given : `K_(sp)(ZnS)=10^(-21),` `K_(a_(1))xxK_(a_(2))` (of `H_(2)S`)=`10^(-20)`]A. `0`B. `1`C. `2`D. `4`

Answer» Correct Answer - B
`K_(sp) = [Zn^(2+)][S^(2-)]`
`[S^(2-)] = (10^(-21))/(0.01) = 10^(-19)`
for `K_(a_(1)), K_(a_(2)) = ([H^(+)]^(2)[S^(2-)])/([H_(2)S])`
`10^(-20) = ([H^(+)]^(2) xx 10^(-19))/(0.1) rArr [H^(+)] = 0.1`
or `pH = 1`


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