The electromotive force of the cell containing two ion-selective electrodes (ISE), Na-ISE vertical bar LiCl (m). PEG 4000 (w), H2O (1 - w)vertical bar CI-ISE has been measured at temperatures of (288.15, 298 15, and 308.15) K as a function of the mass fraction of PEG 4000 (w) in the mixture. w was varied between 0 and 025 in 0.05-unit steps and the molality of the electrolyte (m) was between c.a. (0 03 and 5 8) mol kg(-1) The values of the standard electromotive force. E degrees. were determined using routine methods of extrapolation, together with extended Debye-Huckel and Pitzer equations. The results obtained produced good internal consistency for all the temperatures studied Once E was determined, the mean ionic activity coefficients for LiCl, the Gibbs free energy of transfer from the water to (PEG 4000 + water), and the primary LiCl hydration number were calculated. (C) 2010 Elsevier Ltd All rights reserved