8.0 Solubility and Solubility Product

8.1 Calculating Solubility of a salt

At constant temperature, the maximum number of moles of solute which can be dissolved in a solvent to obtain one litre of solution (i.e. saturated solution) is called solubility.

Solubility does not depend on amount of substance and volume of solution but depends on the following:

1. Temperature

2. Presence of common ion

3. Nature of solvent

At constant temperature, product of concentrations of ions in a saturated solution of substance is called solubility product of that substance. (Saturated solution is that solution in which further dissolution of even a small amount of salt is not possible).

If we add more $AgCl$ to its saturated solution, an equilibrium will be established

$$AgC{l_{(s)}} \rightleftharpoons A{g^ + } + C{l^ - }$$

$$K = \frac{{\left[ {A{g^ + }} \right]\left[ {C{l^ - }} \right]}}{{\left[ {AgCl} \right]}}$$

As $$K\left[ {AgCl} \right] = {K_c} = \left[ {A{g^ + }} \right]\left[ {C{l^ - }} \right]$$

This ${K_c}$ is given a special name, ${K_{sp}}$ i.e., solubility product.

Therefore, if ionic product is less than ${K_{sp}}$, more of salt dissolves.