What `[H^+]` must be maintained in a saturated `H_(2)S` (0.1M) to precipitate CdS but not ZnS, if `[Cd^(2+)]=[Zn^(2+)]=0.1M` initially?
`K_(sp) (CdS)=8 xx 10^(-27)`
`K_(sp) (ZnS)=1 xx 10^(-21)`
`K_(a) (H_(2)S)=1.1 xx 10^(-21)`

Explanation

To solve the problem, we need to determine the concentration of hydrogen ions \([H^+]\) that must be maintained in a saturated \(H_2S\) solution (0.1 M) to precipitate \(CdS\) but not \(ZnS\), given the initial concentrations of \(Cd^{2+}\) and \(Zn^{2+}\) as 0.1 M each. We will use the solubility product constants \(K_{sp}\) for both sulfides and the dissociation constant \(K_a\) for \(H_2S\).

### Step-by-Step Solution:

1. **Write the solubility product expressions**:
- For \(CdS\):
\[
K_{sp}(CdS) = [Cd^{2+}][S^{2-}]
...