Activity coefficients of hydrochloric acid in mixtures with potassium chloride in methanol + water solvents from electromotive force measurements at 298.15 K

Abstract

E.m.f. measurements of the cell, Pt|H₂|HCl(m₁), KCl(m₂), methanol(X), water|AgCl|Ag, have been made at 298.15 K for solvent compositions X= 0, 10, 30, 40 and 45 %(w/w) of methanol, the total ionic strength of each solution being 1 mol kg^–1. The logarithm of the mean ionic molal activity coefficient of hydrochloric acid was found to vary linearly with potassium chloride molality for the systems in which the solvent mixture contained 0, 10 and 30 % methanol. For methanol composition above 30 %, the activity coefficient of the acid was a quadratic function of the salt concentration. Secondary medium effects are discussed in relation to differences in specific ionic interactions for the different electrolyte mixtures in water and in the mixed solvents.