Standard Potentials of M/M+ (M=Li, Na, K, Rb or Cs) Electrodes in Dimethyl Sulphoxide+Water Mixtures at 25°C and Related Ion-Solvent Interactions in the Solvents

Abstract

The standard electrode potentials GE’) of M/M+ (M = Li, Na, K, Rb and Cs) electrodes in aqueous solutions of dimethyl sulphoxide (DMSO) (containing 10, 20, 40 and 60 wt. % DMSO) have been determined at 25°C from e.m.f. measurements of cells of the type: M(Hg)|MCl(/n), solvent] AgCl-Ag, obtaining the activity of metals in amalgams with the help of a similar type of cell in water. The free energies of transfer of MCI, AGt°(MCl) (mole fraction scale) from water to each of these solvents computed from these values and those of sEXg-AgCi obtainable from the literature, rise sharply from Li+ to Na+, and fall from Rb+ to Cs+ with a maximum between Na+ and Rb+. This is considered as due to the superimposition of “ soft-soft ” interactions on the “ electrostatic inter actions ” between the ions and the negative charge centres of hydrogen-bonded solvent complexes. The AG? (I) values for individual ions, obtained by a method of “ simultaneous extrapolation ” arc shown to be largely determined by the “ acid-base ” type ion-solvent interactions as observed in methanol+water mixtures.