Individual activity coefficients of chloride ions in aqueous solutions of MgCl2, CaCl2 and BaCl2 at 298.2 K

The activity coefficients of the individual chloride ions were measured at 298.2 K using a chloride ion selective electrode in aqueous solutions of MgCl2 and CaCl2 up to 3m and BaCl2 up to 1.4m. For these 2:1 electrolytes, the activity coefficients of magnesium, calcium and barium were calculated using values of the mean ionic activity coefficients of the salts. At low electrolyte concentrations, the activity coefficients of the cation are smaller than that of the anion and at higher concentrations the trend is reversed. These results are different from those reported for 1:1 and 1:2 electrolyte solutions studied previously. The activity coefficient of the chloride ion has similar behavior and similar values with Mg2+, Ca2+ or Ba2+ as counterions. Two different methods were used to evaluate the activity coefficients of the individual chloride ions from the emf measurements and the results were undistinguishable within the experimental error. The activity coefficient of the individual ions were correlated with the Khoshkbarchi–Vera equation values and compared with the values obtained from the hydration theory of Bates.