# How do you write the Ksp equation?

Aug 16, 2017

Well, for a start ${K}_{\text{sp"=K_"solubility product}}$, and we use an equilibrium expression.

#### Explanation:

For the sparingly soluble salt, $M X$, we write the equation that represents its dissolution:

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

${K}_{\text{sp}} = \frac{\left[{M}^{+}\right] \left[{X}^{-}\right]}{\left[M X \left(s\right)\right]}$, but $M X \left(s\right)$ as A SOLID cannot express a concentration, and thus the expression simplifies to...

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

Usually standard conditions are specified, because a hot solution can generally hold more solute than a cold one.

For salts of the form $M {X}_{2}$, ${K}_{\text{sp}} = \left[{M}^{2 +}\right] {\left[{X}^{-}\right]}^{2}$. ${K}_{\text{sp}}$
have been measured for a host of insoluble, and semi-soluble ionic salts.