Thermodynamic study of the aqueous (KCl + K2SO4) electrolyte based on potassium amalgam electrode cells

The thermodynamic behavior of the aqueous KCl + K2SO4 electrolyte has been studied on the basis of potential difference measurements on the reversible cell K-amalgam|KCl (mKCl) + K2SO4 (mK2SO4) |AgCl|Ag|Pt. The mean molal activity coefficients γKCl of KCl at molalities mKCl and γK2SO4 of K2SO4 at mK2SO4 in (KCl + K2SO4) mixtures have been determined at various constant values of total ionic strengths I of the mixed electrolyte studied. It has been found that log(γKCl) is a linear function of mKCl at each constant ionic strength studied, thus obeying Harned's rule. The corresponding trace activity coefficients, γ(0)KCl. vary linearly with log I. Using Pitzer's scheme of equations has allowed fair reproduction of the experimental activity coefficients γKCI for I values ≥ 0.5 mol·kg-1 and the evaluation of γK2SO4 in the same range.