Thermodynamics of mixed electrolyte solutions. Comparison of HCl + NH4Cl + H2O and HCl + KCl + H2O

Abstract

Activity coefficients for HCl in HCl + NH₄Cl + H₂O at 20, 25, 30 and 35°C, have been measured at total molalities of 0.1, 0.5, 1, 2 and 3 mol kg^–1 using cells containing hydrogen and silver–silver chloride electrodes. The results at 25°C have been interpreted in terms of the Scatchard treatment of mixed electrolyte solutions and are compared with similar data obtained by Harned and Gancy for HCl + KCl + H₂O. As the single-salt solutions of NH₄Cl and KCl have very similar activity coefficients this comparison provides a test of the hypothesis that the behaviour of mixed solutions is predictable from the properties of the single-salt solutions. These new results show that there are significant differences in the behaviour of the two mixed systems at high molalities.