Standard potentials of I3−/I− and I2/I3− redox couples relative to that of aqueous saturated calomel reference electrode SCE (W), ESCE(w) have been determined in propylene carbonate (PC), N,N-dimethylformamide (DMF), acetonitrile (ACN), and their binary mixtures at 25 °C from potentiometric measurements. The results helped evaluate the standard potentials of the redox couple I2/I− relative to ESCE(w) as well as the related formation constant (Kf) of I3− in these solvent systems. The solvent effects on the formation equilibrium I2+I−\ightleftharpoonsI3− were analyzed in the light of the transfer free energies of I2, ΔGt°(I2), as obtained from solubility measurements of I2 in the solvents, that of I−, ΔGt°(I−), as obtained earlier by use of the widely used TATB reference electrolyte assumption and that of I3−, ΔGt°(I3−), as obtained by subtracting these two contributions from the respective transfer free energies of formation equilibrium in the mixed solvents relative to a chosen reference solvent in each solvent system. The solvation behavior of these individual iodine species viz. I2, I−, I3− was interpreted in terms of involved interaction viz. Born, ion-dipole, ion-induced dipole, dispersion type soft–soft interactions, CTTS complexation and also the cavity effect as computed by the scaled particle theory (SPT).

Absolute standard free energies of transfer AGtO of OH-from water to aqueous mixtures of 2-methoxy ethanol (ME) have been evaluated at 298.15 K by combining the apparent transfer free energies of the lyate ion that were obtained from the standard emf's of the double cell:Hg-HgO/KOH(m), solvent/K(Hg)/KOH(m) waterlHg0-Hg and that from the autoionization constants of these mixed solvents determined by use of the cell comprising H2-and Ag-AgC1 electrodes. The required AGtO values of K+ and H+ were determined earlier using the well-known tetraphenyl arsonium tetraphenyl boride (TATB) reference electrolyte method. These values and their non-Born type contributions in particular, are found to be increasingly positive in water-rich compositions, indicating that the relative stabilization of OH-and the acidity of the mixed solvents decrease with increasing cosolvent composition. These, when compared with those in aqueous mixtures of ethylene glycol and 1,2-dimethoxy ethane, are found to lie intermediate between the latter solvent systems conforming to what is expected from the structural and electronic features of the cosolvents.

Standard free energies of transfer, ΔGt°, of potassium fluoride (KF) from water to aqueous mixtures of dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetonitrile (ACN), 1,2-dimethoxyethane (DME), and 2-methoxyethanol (ME) have been determined at 25 °C from emf measurements performed on the double cell: Pb(Hg)–PbF2/KF(m), solvent/K(Hg)/KF(m), water/PbF2–Pb(Hg). ΔGt° values of F− were obtained from these values using the corresponding values of K+, as obtained earlier by use of tetraphenylarsonium tetraphenylborate reference electrolyte assumption. In each solvent system ΔGt°(F−) values are found to be increasingly positive with cosolvent composition reflecting the pronounced destabilization of F− and their relative order : DME>DMSO≥DMF>>ACN≈ME conforms to what is expected from the relative ‘aproticity’ of the dipolar aprotic cosolvents and that induced in the protic ME by the possible intramolecular H-bonding. The observed larger destabilization of F− compared to OH− in ME–water system has been attributed to the H-bonding effect of the protic cosolvent ME and the reverse behaviour in DME–water and DMSO–water systems to the absence of such effect of these cosolvents. Moreover, tests of Feakins-type extrapolation for assigning individual ion contribution using ΔGt°(KF) values along with those of other potassium halides, provided some important reflections on the inadequacy of such plots made without the data points of F−.

Die Freien Standardenergien für den Transfer von KF aus H2O in wäßrige Gemische von DMSO, DMF, MeCN, 1,2‐Dimethoxyethan (DME) und 2‐Methoxyethanol (ME) werden bei 25°C aus EMK‐Messungen an der Doppelkette A bestimmt.