When ionic solids dissolve, they divide to give their positive and negative ions that make up the solids. These ions become hydrates and have the same relative proportions when in solution and when solid. The more the solid dissolves, the more the ion’s concentration increases. This increase and build-up allows for the reverse reaction to occur. In this phase of the reaction the ions crystallise out in order for the reaction to have a greater chance of occurring. Eventually the rate of dissolving will equal the rate of crystallisation. This is the state of saturation. This can be recognised by a constant colour or constant mass. The solubility product constant, Ksp is g