# What is the definition of Ksp in chemistry?

Aug 11, 2016

#### Explanation:

Essentially, ${K}_{\text{sp}}$ is another equilibrium constant, which measures the solubility of insoluble and sparingly soluble salts.

For an insoluble salt, we may represent its dissolution reaction in this fashion:

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

And its equilibrium reaction may be quantified:

$\frac{\left[{M}^{+}\right] {\left[{X}^{-}\right]}^{2}}{\left[M {X}_{2} \left(s\right)\right]}$ $=$ ${K}_{\text{sp}}$

But you can't have the concentration of a solid, i.e. $\left[M {X}_{2} \left(s\right)\right]$ is removed from the equilibrium expression, to give finally:

$\left[{M}^{+}\right] {\left[{X}^{-}\right]}^{2}$ $=$ ${K}_{\text{sp}}$

${K}_{\text{sp}}$ values have been measured for a host of sparingly soluble and insoluble salts under standard conditions. If ${M}^{+}$ in the above expression were a precious metal, addition of excess ${X}^{-}$ to solution could salt the metal out for recovery.