What is the maximum molarity of `Co^(+2)` ions in `0.1M HC1` saturated with `0.1M H_(2)S. (K_(a) = 4 xx 10^(-21))`. Given: `K_(sp)` of `CoS = 2xx10^(-21)`.

Options

A. `0.10M`
B. `1.00M`
C. `4.48 xx 10^(-11)M`
D. `0.50M`

Answer

D

Explanation

`H_(2)S hArr 2H^(o+) +S^(2-) (K_(a) = ([H^(o+)]^(2)[S^(2-)])/([H_(2)S]))`
`[S^(2-)] = (K_(a)[H_(2)S])/([H^(o+)]^(2)) = (4 xx 10^(-21)xx0.1)/((0.1)^(2)) = 4 xx 10^(-20)M`
For precipitation, `Q_(sp) = K_(sp)`
`[Co^(2+)] = (K_(sp)of CoS)/([S^(2-)]) = (2xx 10^(-21))/(4xx10^(-20)) = 0.05M`