Activity coefficients for the system HCl + CoCl2+ H2O at 298.15 K. Effects of higher-order electrostatic terms

Abstract

Activity coefficients for HCl in the system HCl + CoCl₂ H₂O, at 298.15 K and at constant total ionic strengths of 0.1, 0.5, 1.0, 2.0 and 3.0 mol kg^–1, have been measured by an e.m.f. method. The results have been treated using Scatchard's and Pitzer's equations for mixed electrolyte solutions and activity coefficients for the salt have been derived. Although Scatchard's treatment generally gave a more accurate fit to the experimental data, the fit to Pitzer's equation, though satisfactory, could be significantly improved for the six HCl + NCl₂ systems considered, provided that recognition is given to the contribution of higher-order electrostatic terms beyond the Debye–Huckel approximation to the thermodynamic properties of asymmetrical mixtures.