Role of temperature and pH in Cu(OH)2 solubility

The wide variation in reported cupric hydroxide solubility constants is attributed to the age of the solid, kinetic limitations in approaching equilibrium, and transient formation of basic copper nitrate solids. In situations similar to those where cupric hydroxide solubility constants were determined via precipitation in dilute nitrate solutions, copper nitrate solids (gerhadtite) form first followed by a rapid transition to cupric hydroxide and then a slower transition to tenorite. In solutions containing hydroxide and nitrate as the sole anionic constituents, fresh cupric hydroxide solids control soluble copper concentrations for minutes to days depending on pH and temperature. Thus, although a log K of 9.36 +/- 0.02 was most consistent with the experimental data for Cu(OH)(2) solubility, decreasing log K values from 9.36 [fresh Cu(OH)(2)] to 7.6 [CuO] can be expected with aging as controlled by temperature, pH, and other factors.