Solubility and Solubility Product Determination of a Sparingly Soluble Salt: A First-Level Laboratory Experiment.

A simple experiment was devised to let students determine the solubility and solubility product, Ksp, of calcium sulfate dihydrate in a first-level laboratory. The students experimentally work on an intriguing equilibrium law: the constancy of the product of the ion concentrations of a sparingly soluble salt. The determination of solubility is proposed either in an equimolar precipitation of CaSO4·2H2O, from which the Ksp is obtained, or working with an excess of one of the two reagents.