Ionic association in asymmetric electrolytes

Abstract

The cluster theory of electrolytes previously developed for symmetric salts has been extended to the asymmetric 1 : 2 electrolytes. The intracluster contribution to the configurational Helmholtz energy was calculated for different cluster diameters in order to include this parameter in a Helmholtz-energy minimization procedure. We have calculated the speciation for model asymmetric electrolytes as a function of the strength of the interparticle interactions and compared the results with those for equivalent 2 : 2 model electrolytes. The calculated activity coefficients agree reasonably well with Monte Carlo simulation results for the primitive model. Theoretical predictions for the temperature dependence of the speciation and activity coefficients of 1 : 2 electrolytes are compared with experimental results for MgCl₂ and Na₂SO₄.