Aqueous Solubilities, Solubility Products and Standard Oxidation‐Reduction Potentials of the Metal Sulfides

Available thermodynamic data, incorporating a new free energy of formation for aqueous S 2− of 111 (±2) kJ/mol at 25°C, indicate that solubility products of the insoluble metal sulfide salts are several orders of magnitude smaller than previously considered. Thermodynamic characterization for a variety of soluble and insoluble aqueous metal sulfide systems is reported. Trends in the aqueous solubilities of the alkali salts solubilities are compared and discussed. New aqueous solubility products, , and standard redox potentials, , for over forty metal sulfides are determined. The new values of and at 25°C include: , and . Significant free S 2− occurs only in extremely alkaline media. The suitability of , rather than , based solubility products and redox potentials is discussed and these alternate values determined.