The pressure and temperature effects on the Walden products of Na+, K+, Cs+ and I- in water

Abstract

The conductivities of NaI, KI and CsI in water were measured at 15, 25 and 40℃, up to 1500kg/cm^2. The single ion limiting equivalent conductivities of Na^-, K^-, Cs^- and I^- were calculated at each temperature and pressure. The interactions between these ions and solvent water molecules were deduced from their pressure and temperature coefficients of the Walden products. From the analysis of these quantities on the basis of Zwanzig's solvent relaxation theory, it was revealed that the present experimental results partly showed similar trends as the theory predicted. The discrepancies between the pressure coefficients of the Walden products calculated by this theory and the experimental values may be attributable to the incompleteness of the dielectric continuum model inherent to the theory. As regards I^-, it was found that the pressure coefficient of the Walden product was not so negative as was expected, in spite of its larger crystal radius compared with any alkali metal ion. This may be due to a difference in the orientation of water molecules around the cations and this anion.