Question

Solubility product of a salt $AB$ is $1.0\times {10}^{-8}$ in a solution in which concentration of $A$ is ${10}^{-3}$ M. The salt will precipitate when the concentration of $B$ becomes more than:

• A. ${10}^{-4}$ M
• B. ${10}^{-7}$ M
• C. ${10}^{-6}$ M
• D. ${10}^{-5}$ M

Answer 1

Answer: (D)

${10}^{-5}$ M

$K_{sp}$ of salt AB = [A][B]

Concentration [A] is ${10}^{-3}M$ ---- (given)

$K_{sp}={10}^{-8}$ given

${10}^{-8}={10}^{-3}\left[B\right]$

$\left[B\right]=\frac{{10}^{-8}}{{10}^{-3}}M$

$\left[B\right]={10}^{-5}M$

Concentration of B should not be more then ${10}^{-5}M$