Thermodynamics of electrolytes.: 13.: Ionic strength dependence of higher-order terms;: Equations for CaCl2 and MgCl2

While the original ion-interaction (Pitzer) equations of 1973 were adequate for many electrolytes to the limit of solubility, additional terms are needed for some systems of large solubility. A simple pattern of ionic-strength dependence is proposed for third, fourth, and higher virial coefficients. It is found to be very effective in representing the complex behavior of CaCl2(aq) as well as that of MgCl2(aq) at 25 degrees C. Equations without ion association are presented for each system that are valid for the full range to 11.0 and 5.9 mol-kg(-1), respectively, as well as simpler equations for limited molality ranges.