Experimental activity coefficients in aqueous mixed solutions of KCl and KF at 25 °C compared to Monte Carlo simulations and mean spherical approximation calculations

Abstract

A system of three different ions in solution has been studied experimentally and theoretically. Mean molar ionic activity coefficients have been measured in pure and mixed, aqueous solutions of KF and KCl at 25 °C and 1 atm by means of valinomycin, LaF3 and Ag / AgCl electrodes. More than 200 independent electrometric measurements were considered. The ionic strength varied from 0.0005 to 4 mol dm–3. The activity coefficients were close to unity for pure KF than for KF in equimolar mixture with KCl at the same ionic strength for ionic strengths higher than 1 mol dm–3. The activity coefficients for KCl in pure and mixed solutions could not be statistically separated up to 4 mol dm–3. The Harned coefficients are estimated to be 0 ± 0.0025 dm3 mol–1 for KCl and 0.055 ± 0.025 dm3 mol–1 for KF. The Debye–Hückel limiting law is obeyed within 1.5% in the region from 0.0005 to 0.01 mol dm–3, indicating that the ions involved are small.