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, K sp , and standard redox potentials, E 0 , for over forty metal sulfides are determined. The new values of p K sp and E 0 at 25°C include: Ag 2 S ‐ orthorhombic : 53.6 , − 0.786 V , and HgS ‐ red : 56.4 , − 0.816 V . Significant free S 2− occurs only in extremely alkaline media. The suitability of Δ G f 0 ( HS − ) , rather than Δ G f 0 ( S 2 − ) , based solubility products and redox potentials is discussed and these alternate values determined.