Question

What is the solubility of calcium fluoride in a saturated solution if its solubility product is $3.2\times {10}^{-11}$.

• A. $2.0\times {10}^{-4}$ mole/litre
• B. $12.0\times {10}^{-3}$ mole/litre
• C. $0.2\times {10}^{-4}$ mole/litre
• D. $2\times {10}^{-3}$ mole/litre

Answer 1

The correct option is A $2.0\times {10}^{-4}$ mole/litre

$\underset{S}{Ca{F}_2}\rightleftharpoons \underset{S}{C{a}^{++}}+\underset{(2S{)}^2}{2F^{-}}$

$K_{sp}=4S^3$

$S=\sqrt[3]{3\frac{K_{sp}}{4}}=\sqrt[3]{3\frac{3.2\times {10}^{-11}}{4}}$

$=2\times {10}^{-4}m/l$