The solubility constant (product) (Ks) is
CaF2(s)
Ca2+(aq) + 2F–(aq)
Qs (or IP) = [Ca2+][F–]2
At equilibrium Qs (or IP) = Ks
For CaF2, Ks = 1.5 × 10–10
The form of the equilibrium constant expression depends on the balanced equation for the dissolution reaction as the powers associated with the ion concentrations depends on the relative numbers of cations and anions in the solid.
The solid does not appear because the concentration of solid in itself is constant. Furthermore, increasing the amount of solid in contact with a saturated solution does not affect the ion concentrations.
While the relative equilibrium concentrations of Ca2+ and F– may differ in two saturated solutions at the same temperature, Qs equals Ks for both.
In contrast the solubility s(CaF2) in two saturated solutions differs if, for example, one of the ions arising from dissolution is present before dissolving occurs.
- the equilibrium constant for the reaction in which an ionic solid dissolves to give its ions.
- much less than 1 for sparingly soluble solids like CaF2.
- related to ion concentrations because the magnitude of the equilibrium constant expression is equal to Ks at equilibrium (in a saturated solution)
CaF2(s)
Ca2+(aq) + 2F–(aq)Qs (or IP) = [Ca2+][F–]2
At equilibrium Qs (or IP) = Ks
For CaF2, Ks = 1.5 × 10–10
The form of the equilibrium constant expression depends on the balanced equation for the dissolution reaction as the powers associated with the ion concentrations depends on the relative numbers of cations and anions in the solid.
The solid does not appear because the concentration of solid in itself is constant. Furthermore, increasing the amount of solid in contact with a saturated solution does not affect the ion concentrations.
While the relative equilibrium concentrations of Ca2+ and F– may differ in two saturated solutions at the same temperature, Qs equals Ks for both.
In contrast the solubility s(CaF2) in two saturated solutions differs if, for example, one of the ions arising from dissolution is present before dissolving occurs.