How can Ksp be calculated?
In a saturated solution the solid is in equilibrium with its ions e.g :
The expression for
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
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