Free energies (ΔGt0) and entropies (ΔSt0) of transfer at 25 °C of the nonelectrolyte p-nitroaniline from water to various alcohol + water mixtures have been determined from solubility measurements at seven temperatures from 10–40 °C. Increasing specific solute–solvent interactions have been proposed to interpret the nature of the ΔGt0-composition profiles and the enhanced structure of water in the water-rich mixed solvents has been correlated with maxima in the ΔSt0-composition profiles. The effectiveness of p-nitroaniline as a useful probe for studying solvent structure has been pointed out.

No abstract

Free energies, AGtO and entropies, AS," of transfer of hydrobromic and hydroiodic acids from water to t-butyl alcohol+ water mixtures containing 10, 20, 30 and 50 % t-butyl alchol by weight have been evaluated using the corresponding values of the standard potentials, EO, of silver-silver bromide and silver-silver iodide electrodes in these solvents obtained from electromotive force measurements at seven different temperatures ranging from 5 to 35°C performed on the cell Pt, H,(g, 1 atm)lHX(m), solventlAg-AgX, where X = Br or I. These and the corresponding values for HCl obtained from Eo data given in literature were used to evaluate AGf for individual ions by the " extrapolation procedure ". In contrast with other aqueous organic solvents, humps or kinks in the AG,O against composition profiles occur at water-rich compositions reflecting the strong structural characteristics of this solvent system in that region. The variation of entropies of transfer with composition has been interpreted in terms of marked structure-promotion of water and consequent ion-dehydration at small concentrations of t-butyl alcohol and of the formation of alcohol-water complexes at somewhat higher contents of t-butyl alcohol. The irregular order Br-> I-> C1-in water-rich regions for the entropy profiles is suggested to be due to the formation of charge-transfer complexes of the iodide ion with t-butyl alcohol.

No abstract

The autoprotolysis constants (Ksm) of ethylene glycol in isodielectric acetonitrile + ethylene glycol mixtures have been determined at 25 °C from emf measurements on the cell[Formula: see text]From these values, those of δΔG0, the free energy of ionization of ethylene glycol in these mixed solvents relative to that in pure glycol, have been computed. The nature of variation of δΔG0 with solvent composition has been compared with that in two other mixed systems: water + ethylene glycol and methanol + 1,2-propanediol and the intrinsic differences between the solvation characteristics of the various solvents have been pointed out. The standard free energies of transfer of the glycoxide ion, ΔGt0(OEg−), from pure glycol to acetonitrile + glycol mixtures have also been estimated using ΔGt0(H+) values obtained earlier. The glycoxide ion is increasingly desolvated as the acetonitrile content of the solvent increases, as indicated by increasingly positive values of ΔGt0(OEg−). This behaviour has been compared with those of ΔGt0(H+) and ΔGt0(Cl−) determined previously.