IONIC ASSOCIATION IN ASYMMETRIC ELECTROLYTES

The cluster theory of electrolytes previously developed for symmetric salts has been extended to the asymmetric 1 : 2 electrolytes. The intr acluster contribution to the configurational Helmholtz energy was calc ulated for different cluster diameters in order to include this parame ter in a Helmholtz-energy minimization procedure. We have calculated t he speciation for model asymmetric electrolytes as a function of the s trength of the interparticle interactions and compared the results wit h those for equivalent 2 : 2 model electrolytes. The calculated activi ty coefficients agree reasonably well with Monte Carlo simulation resu lts for the primitive model. Theoretical predictions for the temperatu re dependence of the speciation and activity coefficients of 1 : 2 ele ctrolytes are compared with experimental results for MgCl2 and Na2SO4.