It is probably easiest for me to explain the question in an example. Consider the following chemical formula. #MgF2 (s) ---> Mg2+ (aq) + 2F - (aq)# Pluggingreaction:
$\ce{MgF2(s) -> Mg^{2+} (aq) + 2F- (aq)}$
Plugging this into the formula for the solubility product constant, $K_{sp}=[M^{y+}]^{x}[A^{x-}]^{y}$, we get $K_{sp}=[Mg^{2+}]\times[F^{-}]^{2}$:
$K_{sp}=[\ce{Mg^{2+}}][\ce{F-}]^{2}$.
The solubility product constant for magnesium fluoride is $5.16\times10^{-11}$. To determine molar solubility, so the equation to solve for magnesium and fluoride is $5.16\times10^{-11}=X\times 2X^{2}$$5.16\times10^{-11}=X\times (2X)^{2}$.
$X$ is magnesium and $2X^{2}$$(2X)^{2}$ is fluoride. This is because there are two moles of fluoride for every one mole of $MgFl_{2}$$\ce{MgFl_{2}}$, and one mole of magnesium for every one mole of $MgFl_{2}$$\ce{MgFl_{2}}$. (Please correct me if I'm wrong anywhere.)
But here's whats confusing to me. Why is fluoride denoted as $2X^{2}$$(2X)^{2}$? I know that there are two moles of fluoride per one mole of magnesium fluoride, but why does it need to be denoted by being both multiplied to it'sits coefficient, and raised to the power of that coefficient?
