What is the minimum pH required to prevent the precipitation of ZnS in a solution that is `0.01MZnCl_(2)` and saturated wth `0.10M H_(2)S`?
[Given `K_(sp)=10^(-21),K_(a_(1))xxK_(a_(2))=10^(-20)]`

Options

A. 0
B. 1
C. 2
D. 4

Answer

B

Explanation

`K_(sp)` for `ZnS=[Zn^(2+)][S^(2-)]`
`[S^(2-)]=(10^(-21))/0.01=10^(-19)`
`H_(2)ShArrH^(+)+HS^(-)`
`K_(a_(1))=([H^(+)][S^(2-)])/([HS^(-)])`
`HS^(-)hArrH^(+)+S^(2-)`
`K_(a_(2))=([H^(+)][S^(2-)])/([HS^(-)])`
for `K_(a_(1)).K_(a_(2))=([H^(+)]^(2)[S^(2-)])/(H_(2)S])`
`10^(-20)=[(H^(+)]^(2)xx10^(-19))/0.1implies[H^(+)]=0.1`
or pH=1