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 Mg Cl2 and CaCl2 up to 3m and BaCl2 up to 1.4m. For these 2:1 electrolytes, th e activity coefficients of magnesium, calcium and barium were calculated us ing values of the mean ionic activity coefficients of the salts. At low ele ctrolyte concentrations, the activity coefficients of the cation are smalle r 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 electroly te solutions studied previously. The activity coefficient of the chloride i on has similar behavior and similar values with Mg2+, Ca2+ or Ba2+ as count erions. Two different methods were used to evaluate the activity coefficien ts of the individual chloride ions from the emf measurements and the result s were undistinguishable within the experimental error. The activity coeffi cient of the individual ions were correlated with the Khoshkbarchi-Vera equ ation values and compared with the values obtained from the hydration theor y of Bates. (C) 2001 Elsevier Science B.V. All rights reserved.