Question

Solubility product of the hydroxide $M{\left(OH\right)}_2$ is $4\times {10}^{-12}$. Select the correct statement(s) among the following:

• A. The pH of its saturated solution will be $10.3$
• B. Its solubility will decrease in a buffer medium of $pH=9$
• C. Its solubility will increase in a buffer medium of $pH=1$
• D. Its solubility is unaffected by pH of the medium

Answer 1

Answer: (B), (C)

The correct options are
B Its solubility will decrease in a buffer medium of $pH=9$
C Its solubility will increase in a buffer medium of $pH=1$

${M\left(OH\right)}_2\rightleftharpoons M^2+2{OH}^{-}$

$S$ $S$ $2S$

$\therefore$ $\left[M^{2+}\right]{\left[{OH}^{-}\right]}^2=K_{sp}=4\times {10}^{-12}$

$\Rightarrow S.{\left(2S\right)}^2=4\times {10}^{-12}$

$\Rightarrow {4S}^3=4\times {10}^{-12}$

$\Rightarrow S={10}^{-4}$

$\therefore$ $\left[{OH}^{-}\right]={10}^{-4}M$

$\therefore$ $pH=14-pOH=14-(-log{10}^{-4})=10$

So saturated solution will have $pH$ of $10$

B) In $pH=9$ due to presence of ${OH}^{(-)}$ the solubility will be decreased.

C) In $pH=1$. The presence of higher $H^{+}$ ions take up ${OH}^{(-)}$ in the solution as a result solubility increases.

Answer will be $B$ and $C$.