Thermodynamics of NaCl in aqueous ethylene glycol, acetonitrile, and 1,4-dioxane mixtures from emf measurements at 25°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 solvents, containing up to 0.8 mass fraction of the organic component, with relative permittivities epsilon greater than or equal to 27. The relevant 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 ethylene glycol is observed, which is quite unusual. The Debye-Huckel equation is applicable successfully over the whole range of molalities explored, which extends to the vicinity of the solubility limit of NaCl in 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 previous results employing different methods.