Ionic Equilibria in Mixed Solvents. X. Hydrolysis of Nickel(II) Ion in Dioxane-Water Mixtures

Abstract

Abstract The hydrolytic reactions of nickel(II) ion were studied at 25 °C in water and dioxane-water mixtures containing 3 M (Li)ClO4 as an ionic medium. Emf measurements were carried out in the range of the total nickel(II) ion concentration of 0.02469–0.7891 M in water, 0.02488–0.7996 M in a 0.1 mole fraction (35.21% w/w) dioxane-water mixture and 0.05170–0.9016 M in a 0.2 mole fraction (55.01% w/w) dioxane-water mixture, respectively. Some supplementary measurements were performed in a 0.5 mole fraction (83.02% w/w) dioxane-water mixture. Only the Ni4(OH)44+ complex was found in all solvent systems and its formation constant in log*β44 was −27.32±0.08 (in water), −27.11±0.08 (in a 0.1 mole fraction dioxane-water mixture), and −27.04±0.05 (in a 0.2 mole fraction dioxane-water mixture). In order to test the relative change of the formation consatnt of the Ni4(OH)44+ complex over the whole solvent composition examined, the variation of the formation constant was measured with the continual change of solvent composition at constant Z. Approximate values of the solubility products of Ni(OH)2 and NiOHClO4 precipitates were estimated from maximum values of Z.