The standard partial molar volumes of ions in solution. Part 2. The volumes in two binary solvent mixtures with no preferential solvation

Standard partial molar volumes of ions were obtained from literature data on 1:1 electrolytes in mixtures of propylene carbonate (PC) with acetonitrile (MeCN) and of water (W) with methanol (MeOH) at 298.15 K. The hypothesis was examined that when the solvents in the mixtures do not differ too much in their polarity and/or hydrogen-bonding ability, only negligible preferential solvation occurs in the solvent shell around the ion where electrostriction takes place. Given the solvent-independent intrinsic volume of an ion, the electrostriction, calculated by the shell-by-shell method, permits the examination of this proposition. This hypothesis was indeed validated by the calculated standard partial molar ionic volumes in the dipolar aprotic mixtures and in the protic aqueous methanol.