The equilibrium constant does not explicitly contain the concentration of the insoluble salt, whereas the expression for the solubility-product constant has this concentration in the numerator.

Ksp stands for equilibrium constant of the solubility product. The equilibrium constant for the dissolution of a sparingly soluble salt is the solubility product (Ksp) of the salt. Because the concentration of the salts which are pure solids is constant, it does not appear explicitly in the equilibrium constant expression.

The solubility product, Ksp expression for a salt is the product of the concentrations of the ions, with each concentration raised to a power equal to the coefficient of that ion in the balanced equation for the solubility equilibrium.

The solubility product constant (Ksp) describes the equilibrium between a solid and its constituent ions in a solution. The value of the constant identifies the degree to which the compound can dissociate in water. The higher the Ksp, the more soluble the compound is.