Ionic solutions in the binding mean spherical approximation: Thermodynamicproperties of mixtures of associating electrolytes

Recent advances in the theory of electrolytic solutions are used to describ e osmotic and activity coefficients for aqueous solutions of electrolytes. The thermodynamic properties and also the structure are described by an ext ension of the mean spherical approximation (MSA) that includes association. The association of ions of opposite charges is described using the BIMSA, based on the Wertheim formalism. As was done before, hydration effects are included using a concentration-dependent cation size and permittivity. The theory is used to study aqueous solutions of mixed salts at 25 degrees C. T he procedure yields a very satisfying representation for a number of mixed salts with a common cation where no adjustable cross parameter is needed. F or salts without a common cation, cross parameters are introduced.