M. Uchida et A. Okuwaki, Potentiometric determination of the first hydrolysis constant of gallium(III) in NaCl solution to 100 degrees C, J SOL CHEM, 27(11), 1998, pp. 965-978
The hydrolysis equilibrum of gallium (III) solutions in aqueous 1 mol-kg(-1
) NaCl over a range of low pH was measured potentiometrically with a hydrog
en ion concentration cell at temperatures from 25 to 100 degrees C at 25 de
grees C intervals. Potentials at temperatures above 100 degrees C increased
gradually because of further hydrolysis of the gallium(III) ion, followed
by precipitation. The results were treated with a nonlinear least-squares c
omputer program to determine the equilibrium constants for gallium(III)-hyd
roxo complexes using the Debye-Huckel equation. The log K (mol-kg(-1)) valu
es of the first hydrolysis constant for the reaction, Ga3+ + H2O reversible
arrow GaOH2+ + H+ were -2.85 +/- 0.03 at 25 degrees C, -2.36 +/- 0.03 at 5
0 degrees C, -1.98 +/- 0.01 at 75 degrees C, and - 1.45 +/- 0.02 at 100 deg
rees C. The computed standard enthalpy and entropy changes for the hydrolys
is reaction are presented over the range of experimental temperatures.