Solubility Product
The equilibrium constant for the dissolution of a sparingly soluble ionic solid into its constituent ions.
Formula / equation
Ksp = [A⁺]^m[B⁻]^n
Unit
Various
In depth
The solid itself does not appear in the expression because its activity is constant. Ksp depends only on temperature and allows solubility, precipitation and the effect of added ions to be calculated quantitatively. Comparing Ksp values is only valid between salts of the same ion ratio.
Examples in the real world
AgCl has Ksp = 1.8 × 10⁻¹⁰ giving a solubility of 1.3 × 10⁻⁵ M; CaF₂ has Ksp = 3.9 × 10⁻¹¹.