Studies in some ‘isodielectric’ media. Part III. Standard potentials of M/M+(M = Li, Na, and K) electrodes in methanol–propylene glycol

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Abstract
Standard potentials (sE°) of M/M+(M = Li, Na, or K) electrodes have been determined at 25° in the ‘isodielectric’ methanol–propylene glycol solvent system from the measured e.m.f. values of the cell My(Hg)/MBr(m), solvent/AgBr–Ag. These potentials as well as the known (sE°) values of the AgX–Ag (X = Cl or Br) electrode furnished the standard potentials (sEcell°) of the complete cells comprising the M/M+ and AgX–Ag electrodes. The standard free-energy changes ΔGt°(MX) accompanying the transfer of MX from methanol to the other solvents have been computed and are found to depend chiefly on the ion–dipole interactions, as the ‘electrostatic effect’ is relatively small in this solvent system. The values of ΔGt°(i) for the individual ions, computed from the ‘simultaneous extrapolation’ of the observed linear plots of ΔGt°(MCl) and ΔGt°(KCl–MCl) against (rM +)–1(M = Li, Na, or K), to (rM +)–1= 0, suggest that the cations are methanophilic and that the anions are glycophilic. The variation of ΔGt°(i) values with the solvent composition is found to be in fairly good agreement with what is expected from the consideration of the interaction energies of these ionic species with positive or negative charge centres of the isolated solvent dipoles. Also the values of ΔGt°(H+) for H+ seem to indicate that methanol is more ‘basic’ than propylene glycol.

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