# Question #d71a4

${K}_{s p} = \left[C {a}^{2 +}\right] {\left[{F}^{-}\right]}^{2}$

#### Explanation:

First consider how the compound will dissolve in water - or rather, how it dissociates into its smaller ionic components due to it being an ionic compound,

$C a {F}_{2} \left(s\right) r i g h t \le f t h a r p \infty n s C {a}^{2 +} \left(a q\right) + 2 {F}^{-} \left(a q\right)$

On the left of the equation is the reactant, and on the right, the products. The reactant is a solid, so it will not be included in the solubility equation.

${K}_{s p} = \left[C {a}^{2 +}\right] {\left[{F}^{-}\right]}^{2}$

In one mole of $C a {F}_{2}$, there is one mole of $C {a}^{2 +}$ ions and two moles of ${F}^{-}$ ions. Notice in the equation, the coefficient for the fluoride ions becomes an exponent.