Question

The solubility product of a salt having general formula $MX_{2},$ in water is $4 \times 10^{-12},$ The concentration of $M^{2+}$ ions in the aqueous solution of the salt is

• A. $4.0 \times 10^{-10}\, M$
• B. $1.6 \times 10^{-4}\, M$
• C. $1.0 \times 10^{-4}\, M$
• D. $2.0 \times 10^{-6}\, M$

Answer 1

Answer: (C)

$M X_{2} \rightleftharpoons \underset{s}{M^{2+}}+\underset{2 s}{2 X}$
$K_{s p}=\left[M^{2+}\right]\left[X^{-}\right]^{2}$
If solubility be $s$ then
$K_{ sp } =(s)(2 s)^{2}=4 s^{3}$
$4 s^{3} =4 \times 10^{-12}$
$\therefore s =1 \times 10^{-4} M$
$\therefore M^{2} =s =1 \times 10^{-4} M$