# How can Ksp be calculated?

Dec 6, 2014

In a saturated solution the solid is in equilibrium with its ions e.g :

$C a C {O}_{3 \left(s\right)} r i g h t \le f t h a r p \infty n s C {a}_{\left(a q\right)}^{2 +} + C {O}_{3 \left(a q\right)}^{2 -}$

The expression for ${K}_{s p}$ is:

${K}_{s p} = \left[C {a}_{\left(a q\right)}^{2 +}\right] \left[C {O}_{3 \left(a q\right)}^{2 -}\right]$

We don't include the concentration of the solid as this is assumed constant.

So if we know the concentration of the ions you can get ${K}_{s p}$ at that particular temperature.

Using ${K}_{s p}$ enables you to find the limit of concentration before a solid forms.

An interesting example of this occurs in nature. The organisms in coral can extract calcium and carbonate ions from seawater by active transport. They then excrete them such that their local concentrations cause the value of ${K}_{s p}$ to be exceeded. This shifts the equilibrium to the left causing the calcium carbonate to deposit on the coral.