Question

The solubility product of a sparingly soluble salt $A_{2}B$ is $3.2\times {10}^{-11}$. Its solubility in $mol{L}^{-1}$ is:

• A. $4\times {10}^{-4}$
• B. $2\times {10}^{-4}$
• C. $6\times {10}^{-4}$
• D. $3\times {10}^{-4}$

Answer 1

The correct option is B $2\times {10}^{-4}$

Let $s$ amount of the salt dissolve or dissociate per mole of the salt then:
$A_{2}B\left(solid\right)\leftrightharpoons \underset{2s}{2A^{+}}+\underset{s}{B^{2-}}$
$K_{sp}=\left[2s{]}^2\right[s]$
$s=2\times {10}^{-4}$ M