Activity coefficients of NaCl in aqueous mixtures with high relative permittivity cosolvent: Ethylene carbonate + water at 298.15 K

The mean ionic activity coefficients of NaCl were experimentally determined in ethylene carbonate (EC) + water at 298.15 K from potential difference measurements of the following electrochemical cell containing two ion-selective electrodes (ISEs): Na-ISE|NaCl(m),EC(w),H2O(1-w)|Cl-ISE The molality (m) varied between 0.02 mol·kg^-1 and almost saturation, while the mass fraction of EC in the mixture (w) was varied between 0 and 0.8 in 0.1 unit steps. Values of the standard potential difference, E⁰ (molal scale), were determined using a routine method of extrapolation together with the extended Debye-Hückel, Pitzer, and Scatchard equations. The results obtained produced good internal consistency, within the normal limits of experimental error encountered in these types of measurement. Once E⁰ was determined, the mean ionic activity coefficients of the NaCl, the Gibbs energy of transfer of the NaCl from the water to the EC + water mixture, standard solubility product of NaCl in EC + water, and the NaCl primary hydration number were estimated. The results were comparatively analyzed with those of the NaF previously obtained in similar mixtures.