The transference numbers of KCl aqueous solution under pressure

Abstract

The transference numbers of K^+ ion in KCl aqueous solutions have been determined at high pressure up to 1, 300kg/cm^2 at the concentration from 0.01 to 0.1N at 25℃ and at 0.02N at 15 and 40℃ by the moving boundary method. The movement of the boundary was detected by the resistance measurement. Cadmium chloride was used as an indicator solution. The transference numbers at infinite dilution at 25℃ were calculated by the empirical equation of Longsworth. The K^+ ion transference numbers decrease with the increase in pressure in all cases. This decreasing tendency becomes weaker with the increase in temperature. Besides, the K^+ ion transference number increases slightly with the increase in temperature at 1500kg/cm^2, while it decreases with the increase in temperature at atmospheric pressure. The ion-water interaction of K^+ ion is mostly dominated by the electrostriction, while the ion-water interaction of Cl-ion involves the hydrogen bond additionally. It is considered that the hydrogen bond in the hydration shell of Cl^- ion is broken with the increase in pressure and/or temperature as that in pure water. That is to say, the hydration of Cl^- ion decreases to a small degree with the increase in pressure and/or temperature.