Conductance of alkali metal ions in compressed water at 25 °C

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Abstract
Limiting molar conductances (λ0) of Li+, K+, Cs+, and Cl− ions in water have been determined at 25 °C as a function of pressure up to 2000 kg cm−2 from the measured conductances (Λ) of LiCl, KCl, and CsCl. In the pressure range investigated, λ0(Li+) increases, λ0(Cs+) decreases, and λ0(K+) and λ0(Cl−) have a maximum at 520 and 1230 kg cm−2, respectively. The drag coefficient (Δζ) subtracted by that due to Stokes’ law for perfect slip (4πηR) is obtained for the alkali metal ions and compared with that predicted by the Hubbard and Onsager (HO) dielectric friction theory over the pressure range. The observed decrease in Δζ with pressure for the small ion Li+ can be explained by the HO theory, but the increase for the large ion Cs+ shows a limitation of the continuum theory. The latter trend suggests that Cs+ ions may possibly pass through larger unoccupied cavities in the open structure of water which is less developed at higher pressures. Δζ for the medium‐sized ion K+ is constant, which seems to result from the balance of the dielectric friction and the passing‐through‐cavities mechanism.

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