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 {yMgCl2+(1−y)NaCl}(aq) and {yMgCl2+(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 II), 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 θ and ψ 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.