Solubility and solubility product of crystalline Ni(OH)(2)

The solubility of crystalline Ni(OH)(2) was studied in solutions of 0.01M NaClO4 with pH ranging from 7 to near 14. Equilibrium was approached both from over- and undersaturation, and the equilibration times extended from 3 to 90 days. The solubility of Ni(OH)(2)(c) in the pH range of approximately 7 to 11.3 was effectively modeled by including aqueous Ni2+ and NiOH+ species. Values of the logarithm of the thermodynamic equilibrium constants for the reactions [Ni(OH)2(c) Ni2+ + 2OH(-)] and [Ni2+ + OH- reversible arrow Ni(OH)(+)] were determined to be -16.1 +/- 0.1 and 5.65 +/- 0.10, respectively. These data, in conjunction with Fitter ion interaction parameters given in the literature, were used to model the reported solubilities of Ni(OH)(2)(c) in chloride, sodium acetate, and potassium chloride solutions. The model predictions for these systems were in excellent agreement with the experimental data from the literature.