Correlation of activity coefficients in electrolyte solutions using a Kelvin hard sphere-mean spherical approximation (K-MSA) model

A hard sphere system, using Kelvin tetrakaidekahedron cells, coupled with t he mean spherical approximation (MSA), accurately correlates the mean ionic activity, and the individual activities of ions, in aqueous solutions of s ingle 1:1 electrolytes. For the mean ionic activity coefficients, the diame ter of the anion is fixed at the Pauling value and the cation diameter is a function of composition. Hydrated diameters of cations are realistic in co mparison with Pauling values, and the like and unlike ionic pair correlatio n functions at contact value are positive in the whole concentration range. The use of a simpler version of the MSA has little effect on the results a nd dramatically reduces the computation time. The results obtained from the Kelvin mean spherical approximation, K-MSA model, compare favorably with t hose of other models. The correlation of individual ionic activity coeffici ents requires composition-dependent diameters for the cation and anion.