Question

Solubility product of salt $AB$ is $1{\times 10}^{-8}{M}^2$ in a solution, on which the concentration of $A^{+}$ ions is ${10}^{-3}M$. The salt will precipitate when the concentration of $B^{-}$ ions is kept:

• A. Between ${10}^{-8}M$ to ${10}^{-7}M$
• B. Between ${10}^{-7}M$ to ${10}^{-8}M$
• C. $>{10}^{-5}M$
• D. $<{10}^{-8}M$

Answer 1

The correct option is C $>{10}^{-5}M$

Precipitation of salt will occur when $K_{sp}<\left[A^{+}\right]\left[B^{-}\right]$.

It is given that $\left[A^{+}\right]={10}^{-3}M$.

So ${10}^{-8}<\left({10}^{-3}\right)\left[B^{-}\right]$

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