Problem $2$:

Fluoride is commonly added to drinking water to help prevent tooth decay. Assume the water already contains $16m\frac{g}{l}$ of the fluoride ion. What would be the concentration of the fluoride ion F$-$ when the calcium fluoride $Ca{F}_2$ is added to the solution $(Ca{F}_{2}harrC{a}^{2+}+F^{-})$and the temperature is $25C.$ The solubility product constant is $K_s={10}^{-10\mathrm{.}50}.($Make sure to balance the reaction$)$