Molar solubility is the number of moles of a substance (the solute) that can be dissolved per liter of solution before the solution becomes saturated. It can be calculated from a substance's solubility product constant (Ksp) and stoichiometry. The units are mol/L, sometimes written as M.
Contents
Derivation
Given excess of a simple salt AxBy in an aqueous solution of no common ions (A or B already present in the solution), the amount of it which enters solution can be calculated as follows:
The Chemical equation for this salt would be:
where A, B are ions and x, y are coefficients...
Simple calculation
If the solubility product constant (Ksp) and dissociation product ions are known, the molar solubility can be computed without the aforementioned equation.
Example
Ionic substance AB2 dissociates into A and 2B, or one mole of ion A and two moles of ion B. The soluble ion dissociation equation can thus be written as:
where the corresponding solubility product equation is:
If the initial concentration of A is x, then that of B must be 2x. Inserting these initial concentrations into the solubility product equation gives:
If Ksp is known, x can be computed, which is the molar solubility.