Emf. measurements of the cell, Na-ISE | NaCl(m), CH3OH(Y), H2O (100-Y) | Cl-ISE (solid state), were carried out at the different molalities of NaCl in the mixtures of CH3OH-H2O containing 0, 20, 40, 60, 80, 90 and 100 of wt.(%) of CH3OH, resp. at 298.15K. Calcns. of standard cell potential of each condition were made by using the extended Debye-Hueckel equation and the Pitzer equation. The calculating results of standard potential of two equations were in good agreements with each other. The mean activity coefficients of NaCl were obtained from the standard potentials by means of the Pitzer equation. The Pitzer-Simonson equation was applied to the system containing ionic pairs. According to this equation the association constants of NaCl in mixtures of CH3OH-H2O are estimated from the experimental emf. data. It showed that NaCl may be associated in 60% of CH3OH. Finally the standard molar Gibbs free energies of transfer, DG癵, of the NaCl from water to methanol-water mixed solvents were calculated using the E?of the cell (I).

Key words: WATER, METHANOL, SODIUM CHLORIDE, ACTIVITY COEFFICIENT, ASSOCIATION CONSTANT