Thermodynamics of mixed electrolyte solutions. VI. An isopiestic study of a pseudo-ternary system: NaCl?KCl?MgCl2?H2O at 25°C

Activity coefficients for magnesium chloride in the aqueous pseudo-ternary system sodium chloride-potassium chloride-magnesium chloride were derived from isopiestic measurements at 25°C. The isopiestic data were treated by both McKay-Perring and Scatchard methods, and results obtained agree fairly well over the ionic strength range of 1–6. At constant ionic strength, the activity coefficient of MgCl₂ increased with addition of other salts. Interaction coefficients were obtained from Scatchard's and Friedman's formalisms. The excess free energy of mixing was calculated and compared with similar systems.