Ionic solutions under high pressures III : pressure and temperature effects on the mobilities of K+ and Cl- ions

Abstract

The electrical conductivity of aqueous solutions of KCl has been measured as a function of pressure up to 5, 000 atm for 8 dilute concentrations(10^-4～10^-3_N) at the temperatures of 15, 25 and 40℃. At each pressure and temperature the equivalent conductance Λ has become a linear function of the square root of the concentration in this concentration range with the slope obtained in good agreement with that calculated from the Onsager limiting equation for conductance. The curve of the limiting equivalent conductance Λ° vs pressure has a maximum at all the temperatures. The pressure of the maximum conductance (P_m, con) of KCl decreases with increasing temperature, approaching zero at about 45℃, as the pressure of the minimum viscosity of water (P_m, vis) decreases with the rise in temperature. However, P_m, con has been found to be higher than P_m, vis at all the temperatures, as in the case of [Co(NH_3)_6]_2(SO_4)_3. The Walden product Λ°η° increases with an increase in pressure at each temperature. Both the relation, P_m, con >P_m, vis and increase in Λ°η° with increasing pressure can be understood by considering that the hydrated ions have their hydration shell compressed by pressure with their hydration number kept constant. The Arrhenius activation energies of migration of K^+ and Cl^- ions at infinite dilution were calculated and compared with those of the viscous flow of water at high pressures at 25℃.