Question

A solution of saturated $Ca{F}_2$ is found to contain $4.1\times {10}^{-4}M$ fluoride ion. Calculate the $K_{sp}$ of $Ca{F}_2$. Neglect hydrolysis.

Answer 1

Saturated Solution of $Ca{F}_2$ have $\left[F^{-}\right]=4\times {10}^{-4}$

$Ca{F}_2\leftrightharpoons C{a}^{2+}\left(S\right)+2F^{-}\left(2S\right)$

let $S$ be solubility, $\therefore 2S=4\times {10}^{-4}$

$4S^3=Ksp$

$K_{sp}=4(2\times {10}^{-4}{)}^3$

$K_{sp}$ of $Ca{F}_2$ solution $=3.2\times {10}^{-12}$