Determination of Ion Activity Coefficients from the Measurement of Membrane Concentration Potentials–Activity Behavior of Alkali-metal Cations in Aqueous Solutions at 25°C

Abstract

Abstract The membrane concentration potentials across a permselective sulfonated polystyrene collodion-base membrane were measured with aqueous solutions of alkali-metal salts at 25.0°C. By assuming the ideal behavior of the membrane, the activity coefficients of the critical cations were determined from the membrane concentration potentials at ionic strengths higher than 0.01. The ion activity coefficients of alkali-metal cations were found to follow the order Li+>Na+>K+ for the chlorides, nitrates, perchlorates, and sulfates. The order of activity coefficients of Na+ in different halide solutions was bromide>chloride>fluoride. Considerable differences were observed between the individual and mean activity coefficients at ionic strengths higher than 0.01. The individual ion activity coefficients determined from the experimental data were analysed by means of the extended Debye-Hückel eauation.