Ionic solutions under high pressures I : pressure and temperature effects on the mobilities of the Co(NH3)6 3+ and SO4 2- ion

Abstract

Ionic conductances of aqueous solutions of hexamminecobalt (III) sulfate, [Co(NH_3)_6]_2(SO_4)_3, have been measured as a function of pressure up to 5, 000 atm for seven dilute concentrations (about 10^-4N) at the temperatures of 15, 25 and 40℃. At each pressure and temperature was satisfied the Kohlrausch relationship between Λ and √<C>. The curve of the limiting equivalent conductance, Λ°vs pressure has a maximum point at about 800 atm even at a high temperature of 40℃, where the viscosity of water increases monotonously, without any minimum, as pressure increases. And the Walden product Λ°η° increases with increasing pressure at each temperature. These phenomena may suggest the decrease in radii of hydrated ions with increasing pressure. Quantitatively analyzing the effective radii of hydrated ions under high pressures with the Robinson-Stokes methods, it is found that this suggestion is reasonable and the hydration numbers of the hydrated ions are invariant within the experimental error as pressure increases. Arrhenius activation energies of ionic migration were calculated and compared with those of viscous flow of water under high pressures.