THERMODYNAMICS OF AQUEOUS GALLIUM CHLORIDE - APPARENT MOLAR VOLUMES AND HEAT-CAPACITIES AT 25-DEGREES-C

Apparent molar volumes and heat capacities of aqueous GaCl3 have been measured at 25°C in binary GaCl3 solutions up to 3 mol-kg-1, and in ternary GaCl3-HCl solutions, containing 0.1345 mol-kg-1 HCl to suppress hydrolysis, up to a concentration of 1 mol-kg-1 GaCl3. Using the Pitzer interaction model for the excess properties, and using ridge regression for the derivation of physically meaningful regression parameters, the measurements yield the following results for the standard molar properties and Pitzer parameters at 25°C: V0(GaCl3)=12.85 cm3-mol-1;β0v(GaCl3)=1.10×10-4 kg-mol-1-J-1-cm-3; βv1(GaCl3)=2.12×10-3 kg-mol-1-J-1-cm3; Cv(GaCl3)=1.34×10-5 kg2-J-1-cm3; Vo(GaOHCl2)=13.84 cm3-mol-1; Cop(GaCl3)=-480.8 J-K-1-mol-1; βJ0(GaCl3)=-8.02×10-6 kg-mol-1-K-2; βJ1(GaCl3)=0.73×10-4 kg-mol-1-K-2; CJ(GaCl3)=-2.52×10-6 kg2-mol-2-K-2; Cp0(GaOHCl2)=20.4 J-K-1-mol-1. The latter parameter has only mathematical significance, its physical meaning is unclear. Comparison of the present experimental results for the standard molar properties of Ga3+ with semi-empirical correlations casts doubt upon the general validity of these correlation methods for trivalent cations. © 1990 Plenum Publishing Corporation.