Preferential solvation of ions and solvent transport
| Autor: | D. Feakins, R. O'Neill, E. Waghorne |
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| Rok vydání: | 1982 |
| Předmět: | |
| Zdroj: | Pure and Applied Chemistry. 54:2317-2326 |
| ISSN: | 1365-3075 0033-4545 |
| DOI: | 10.1351/pac198254122317 |
| Popis: | In the common binary aqueous mixtures, for example dioxan + water, an ion induces a non-random equilibrium distribution of solvent molecules such that close to the ion one solvent component is in excess of its concentration in the bulk. Thermodynamic, spectroscopic and transport properties of the solution are influenced by this preferential solvation. We concentrate here on the transport of one solventI comp6nint WTith ripect to the other in the field of the ion and show how diffusion and transport measurements can be combined to obtain the transport number of water, say, with respect to the non-aqueous solvent component, It can be shown that n = N LLLJ w (l/q) + (l/q where N is the total dynamic solvation number, 1 is the ratio of water to non-aqueous component in the transported solvent and q the corresponding ratio in the bulk. Values of n for alkali-metal and halide ions in solutions of high water content containing raffinose, dioxan, acetone, methanol, allyl alcohol, tertiary butanol, dimethysulphoxide and glycine are presented. The values in the 0.75% (W/W) raffinose + water system probably approach N in .+ + + + pure water closely; they are Li (16) Na (10) K (6) Cl (4) and H (1). In the remaining systems these figures are reduced by competition of the organic molecule for solvation of the ion; is seen to be influenced by the ion-molecule (acid-base) interaction, steric and kinetic effects. Glycine solvates both cations and anions preferentially; DMSO and tertiary butanol solvate the halide ions preferentially. Very marked changes in as a function of composition (q) in the DMSO + water and dioxan + water systems occur for some ions. These can be explained in terms of changes in N and l/q with the structure of the mixed solvents. |
| Databáze: | OpenAIRE |
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