Osmotic and activity coefficients of strongly associated electrolytes over large concentration ranges from chemical model calculations

Abstract

Abstract Association in electrolyte solutions is investigated in the framework of chemical models. Several ways for the calculation of the association equilibria are proposed to explain the measured thermodynamic excess functions. The MSA-MAL (mean spherical approximation - mass action law),an extended Bjerrum model, yields a reliable description of the measurements for moderate association mainly of electrostatic origin. In connection with expressions for the MSA activity coefficients and with the use of the Ebeling association constant a reliable explanation is possible with a single parameter which is the minimum contact distance R of the free ions. For stronger association (low degrees of dissociation α) the solution of the associative mean spherical approximation (AMSA) reproduces satisfactorily the measured data up to high concentrations. The results of these two approaches are compared to experimental data and discussed with regard to their interconnections and limitations. Comparison is also made with other approaches of the literature.