Abstract

The electromotive force, E, of the cell containing two ion-selective electrodes (ISE) Na-ISE | LiCl(m), ethanol (Y), H 2O(100-F) | Cl-ISE has been measured at a temperature of 298.15 K as a function of the weight percentage Y of ethanol in a mixed solvent. Y was varied between 0 and 80% in 20-unit steps, and the molality of the electrolyte (m) was between 0.02 and 4 mol kg -1, approximately. This electrode system was previously checked and calibrated by measuring the activity coefficients of LiCl in 0, 20, and 40% methanol-water and comparing them with literature values. The values of the standard electromotive force, E 0 (molal scale), were determined using routine methods of extrapolation (Debye - Hückel and Pitzer equations). The results obtained produced good internal consistency within the normal limits of experimental error encountered in these types of measurements. Once E 0 was determined, the mean ionic activity coefficients for LiCl, the free energy of transfer from the water to the alcohol - water mixture, and the primary LiCl hydration number were calculated. The variation of these magnitudes with the composition of the mixture is discussed in terms of the ion-solvent and ion - ion interactions and their changes with the properties of the medium. ©2008 American Chemical Society.