APPLICATION OF THE MEAN SPHERICAL APPROXIMATION AND ION ASSOCIATION TO DESCRIBE THE ACTIVITY-COEFFICIENTS OF AQUEOUS 1 1 ELECTROLYTES/

The unrestricted version of the mean spherical approximation has been applied to describe the concentration dependence of the mean ionic act ivity coefficients for 12 aqueous electrolyte solutions for which exte nsive permittivity data are also available. By using the actual solven t permittivity rather than that of the pure solvent, it is shown that this primitive model fits the experimental data in almost all cases to the maximum concentrations for which the permittivity can be describe d by the use of three adjustable parameters, namely, an effective ioni c diameter, sigma(+) or sigma(-), the effective ion pair diameter sigm a(ip), and the association constant K-as for ion pair formation. The v alues of K-as obtained are discussed with respect to results from expe riments reported in the literature. (C) 1997 Elsevier Science S.A.