Studies in ion solvation in non-aqueous solvents and their aqueous mixtures. Part 14.—Free energies of transfer of the alkali-metal chlorides from water to 10–99 %(w/w) methanol-water mixtures at 25°C

The cell Ag-AgCl | MCl(ms), S | M(Hg)| MCl(mw), W | AgCl-Ag has been used to determine the standard molar free energies of transfer, ΔG°t, of the alkali-metal chlorides, MCl, from water, W, to 10–99 %(w/w) methanol-water mixtures, S. ΔG°t rises from Li+ to Na+ and falls from Rb+ to Cs+, with a maximum between Na+ and Rb+ whose position depends on the solvent composition This behaviour is discussed in terms of the “acid-base” theory of ionic solvation. Whilst a “non-electrolytic” effect may be important, the results are also consistent with a more general treatment in terms of “hardness” and “softness” in the acids and bases.