Thermodynamic properties of the mixed electrolyte systems {yMgCl2 + (1-y)NaCl}(aq) and {yMgCl2 + (1-y)CaCl2}(aq) at 298.15 K

Aqueous mixtures of electrolytes of magnesium with sodium or calcium {yMgCl(2) + (1 - y)NaCl}(aq) and {yMgCl(2) + (1 - y)CaCl2}(aq) have been studied using the hygrometric method at 298.15 K. The water activities of each system are measured at total molalities from 0.2 mol kg(-1) to saturation for different ionic strength fractions (y) Of MgCl2 with y = 0.33, 0.50 and 0.67. The results allow the deduction of osmotic coefficients. Experimental results are compared with calculations using the Zdanovskii-Stokes-Robinson (ZSR), Kusik and Meissner (KM), Robinson and Stokes (RS), Lietzke and Stoughton (LS 11), and Reilly-Wood-Robinson (RWR) rules, and the Pitzer model. The results show that a good accuracy is obtained with the Pitzer model. As a matter of fact, in the Pitzer model the parameters theta and psi are adjusted. From these measurements, the mixing ionic parameters are determined and used to predict the solute activity coefficients in their mixtures. The excess Gibbs energies are also determined. (c) 2005 Elsevier Ltd. All rights reserved.