Emf. measurements for the cells (A) Pt, H2(1 atm)|HCl(mA), 1,2-C3H5(OH)2(X), H2O(1-X)|AgCl-Ag and (B) Pt, H2(1 atm)|HCl(mA), NaCl(mB), 1,2-C3H5(OH)2(X), H2O(1-X)|AgCl-Ag were made at 5-45?for ionic strengths 0.1-3.0 and X = 0.05. The standard potential of the AgCl-Ag electrode in the mixed solvents is obtained from the cell (A). Activity coefficients gA of HCl in the HCl-NaCl-1,2-C3H5(oH)2-H2O system were obtained from the cell (B). The results show that HCl obeys the Harned rule and that log gA is a linear function of temperature The primary, secondary, and total medium effects were calculated The results indicate that related partial molar enthalpies of HCl obey a similar Harned rule.

Key words: MULTICOMPONENT SYSTEM, WATER, THERMODYNAMIC PROPERTIES, ACTIVITY, ELECTROMOTIVE FORCES, ELECTROLYTE, SODIUM CHLORIDE, ENTHALPY, HYDROGEN CHLORIDE, SOLUTION THEORY