Concept preview

What you will be able to do

1. 01Describe dissolving as a dynamic equilibrium
2. 02Distinguish saturated, unsaturated and supersaturated solutions
3. 03Define and convert solubility and molar solubility

You already know that a saturated solution holds the maximum amount of dissolved solute. In Chemistry 12 we look at what is really happening at the surface of the undissolved solid. Ions are constantly leaving the solid and entering solution (dissolving), and at the same time dissolved ions are constantly returning and rebuilding the solid (crystallising). When the solution is saturated, these two opposing processes occur at exactly the same rate, so the amount dissolved never changes. This is a dynamic equilibrium, identical in principle to the gas-phase equilibria of the previous chapter: $\text{rate}_{\text{dissolving}} = \text{rate}_{\text{crystallising}}$.