Solvent isotope effect on mobilities of potassium and chloride ions in water at high pressure. II. A low temperature study

Abstract

Limiting molar conductances of the K+ and Cl− ions in heavy and light water have been determined at 5 °C as a function of pressure up to 1500 kgf cm−2 (1 kgf cm−2=0.9807×105 Pa) from the measured conductances and transference numbers of KCl. The residual friction coefficients (Δζ) are obtained for the cation and anion in D2O and H2O by using the determined limiting conductance and the bulk viscosity of solvent, and they are compared with the corresponding values predicted by applying the Hubbard–Onsager (HO) dielectric friction theory at various pressures below 1000 kgf cm−2. At atmospheric and high pressures, the solvent isotope and temperature effects on Δζ observed for the K+ ion are qualitatively in agreement with the theoretical prediction. However, the slightly positive pressure coefficients of Δζ(K+) are obtained in both solvents at 5 °C contrary to the theoretical prediction. Furthermore, Δζ(K+) in D2O at 5 °C is smaller than the theoretical one. These results suggest that another mechanism such as the passing through cavities one plays a more important role in ion migration of the K+ ion at lower temperatures and in D2O. On the other hand, the reverse solvent isotope and temperature effects on Δζ(Cl−), and the negative values of Δζ(Cl−) are found. These anomalies cannot be explained by the continuum theory.