Studies in ‘isodielectric’ media. Part II. Autoprotolysis constants of methanol–propylene glycol at 25 °C

Abstract

The autoprotolysis constants (K_s) of a series of approximately ‘isodielectric’ media comprising methanol and propylene glycol (PG) have been determined at 25° from the e.m.f. measurements of the cell: Pt, H₂(g, 1 atm)| NaS(m₁), NaCl(m₂), solvent|AgCl–Ag. Since the ‘electrostatic effect’ arising from the little difference in dielectric constant values is negligibly small, the standard free-energy changes accompanying the transfer of solvent molecules acting as an acid as well as a base, from methanol to the solvent, have been shown to be dictated by the intrinsic acidity and basicity of the solvents. The results suggest that the acidity of the mixed solvents increases and the basicity decreases, as the proportion of PG is increased.