Thermodynamics of aqueous gallium chloride: Activity coefficients in dilute and high chloride solutions with consideration of the effects of hydrolysis and chloride complex formation

Abstract

An attempt is made to evaluate the Pitzer parameters for activity and osmotic coefficients in aqueous GaCl 3 solutions on the basis of literature data. Anion exchange data demonstrate the necessity of incorporating the formation of the GaCl − 4 complex and allow estimation of the following parameters at 25°C: β 0 (GaCl 3) = 0.3761 kg mol −1; β 1 (GaCl 3) = 15.72 kg mol −1; C(GaCl 3) = −0.0034 kg 2 mol −2; log K 4 = −8.28 for the reaction Ga 3+ + 4Cl − ⇌ GaCl 4 −; β 0 (HGaCl 4) = 0.0641 kg mol −1; β 1 (HGaCl 4) = 0.2945 kg mol −1; C (HGaCl 4) = 0.0004 kg 2 mol −2. The latter β 1 and C parameters are taken equal to those of HCl. These results indicate that at 25°C GaCl 4 − complex formation in nearly pure GaCl 3 solutions becomes important only above concentrations of about 4 mol kg −1 GaCl 3. In solutions with low Ga/Cl ratio's, complexation is dominant above chloride concentrations of about 8 mol kg −1. With increase in temperature complexation extends to lower concentrations. Renewed evaluation of potentiometric data confirms that the NBS-value of −159 kJ mol −1 for the standard Gibbs free energy of formation of aqueous Ga 3+ is a reasonable estimate.