EXPLICIT APPROXIMATIONS OF THE MEAN SPHERICAL APPROXIMATION MODEL FORELECTROLYTE-SOLUTIONS

Two alternative explicit approximations to the mean spherical approxim ation (MSA) for electrolyte systems with ions of different sizes and e lectrostatic charges are presented. The proposed approximations enable easy derivation of other thermodynamic properties due to electrostati c interaction. Explicit expressions are desirable when an equation of state approach is used for electrolyte systems. In this study, the app roximations are used to calculate osmotic coefficients and chemical po tentials for a wide range of conditions. The deviations of the results from the full MSA are calculated and compared with those obtained by using the approximation of Harvey et al.8 Both the proposed explicit f orms are generally better, particularly for unequal charge ion mixture s with high ratio of ion diameters. One of the proposed forms gives ch emical potentials very close to those obtained by using full MSA.