Thermodynamic properties of multicomponent electrolyte solutions in mixed solvents. 5• HCl + NaCl + urea + water at 278.5–318.15 K

This paper reports electromotive force measurements of the cells[Formula: see text]and[Formula: see text]in mixed solvents of urea, mole fraction x = 0.05, at five temperatures from 278.15 to 318.15 K. The standard potentials of Ag–AgCl electrode in mixed solvents were obtained from the emf of cell (A) for HCl of molality mA from 0.02 to 0.11 mol kg−1, both by extrapolation on the basis of an extended Debye–Hückel equation and by a polynomial approach proposed in this paper on the basis of Pitzer's electrolytic solution theory. The standard free energies of transfer for HCl are discussed. The activity coefficients of HClγA in HCl + NaCl + urea + water have also been obtained from the emf of cell (B) at constant total ionic strength I = 0.5, 1.0, 1.5, and 2.0 mol kg−1. The experimental results show that HCl obeys Harned's rule and log γA is a linear function of absolute temperature T. They also indicate that the relative partial molar enthalpy of HCl obeys a similar Harned's rule.