Question

$K_{sp}$ of $CuS,{Ag}_{2}S$ and $HgS$ are ${10}^{-31},{10}^{-44}$ and ${10}^{-54}$ ${mol}^2$ ${litre}^{-2}$ respectively. Select the correct order for their solubility in water.

• A. ${Ag}_{2}S>HgS>CuS$
• B. $HgS>CuS>{Ag}_{2}S$
• C. $HgS>{Ag}_{2}S>CuS$
• D. ${Ag}_{2}S>CuS>HgS$

Answer 1

The correct option is D ${Ag}_{2}S>CuS>HgS$

For ${Ag}_{2}S$, $4s^3=K_{sp}={10}^{-44}$

So solubility $s=1.35\times {10}^{-15}$

For $CuS$, $s^2=K_{sp}={10}^{-31}$

$s=3.16\times {10}^{-16}$

For $HgS$, $s^2=K_{sp}={10}^{-54}$

$s={10}^{-27}$

So order of solubility in water,

$A{g}_{2}S>CuS>HgS$