Studies in ion solvation in non-aqueous solvents and their aqueous mixtures. Part 17.—Free energies of transfer of alkali-metal chlorides from water to 10–40 %(w/w) dioxan + water mixtures, and of potassium bromide and iodide to the 20 % mixture, at 25°C

Abstract

The cell Ag–AgX | MX(m_s), S | M(Hg)| MX(m_w), W | AgX–Ag, has been used to determine the standard molar free energies of transfer, ΔG^°_t, of the alkali-metal chlorides from water to 10, 20 and 40 %(w/w) dioxan + water mixtures and of potassium bromide and iodide to the 20 % mixture. Results from an earlier Part showing ΔG^°_t for the transfer from water to 20 % dioxan for the alkali-metal chlorides to be linear with respect to the reciprocal of cation radius are withdrawn. Instead it is found for all transfers, as in the methanol + water system, that ΔG^°_t(Li⁺Cl^–) < ΔG^°_t(Na⁺Cl^–) but that ΔG^°_t(Rb⁺Cl^–) > ΔG^°_t(Cs⁺ Cl^–); this is explained in terms of the “acid-base” theory of ionic solvation. Tests of additivity show the new data to be highly consistent with previous work.