THERMODYNAMICS OF NACL IN AQUEOUS ETHYLENE-GLYCOL, ACETONITRILE, AND 1,4-DIOXANE MIXTURES FROM EMF-MEASUREMENTS AT 25-DEGREES-C

The electromotive force of the amalgam cell {NaxHg1-x\NaCl(m)\AgCI\Ag} has been measured at 25 degrees C as a function of the mole fraction x of Na in amalgams and of the molality m of NaCl in (ethylene glycol + water), (acetonitrile + water), and (1,4-dioxane + water) mixed solv ents, containing up to 0.8 mass fraction of the organic component, wit h relative permittivities epsilon greater than or equal to 27. The rel evant standard molal electromotive forces E-m(o) have been determined, together with the mean molal activity coefficient gamma(+/-) of NaCl as a function of its molality. In the case of (ethylene glycol + water ) mixtures, a linear dependence of E-m(o) on the mass fraction of ethy lene glycol is observed, which is quite unusual. The Debye-Huckel equa tion is applicable successfully over the whole range of molalities exp lored, which extends to the vicinity of the solubility limit of NaCl i n each solvent. The dependence of the standard emf on the logarithm of the volume fraction of water in the aqueous-organic solvent mixtures have been analyzed in terms of Feakins and French's theory, leading to a primary hydration number 7.2 for NaCl, in good agreement with previ ous results employing different methods.