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

The mean ionic activity coefficients of NaBr 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|NaBr(m), EC(w), H2O(1-w)|Br-ISE The molality (m) varied between 0.04 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-Rard-Archer, and Scatchard equations. The results obtained produced good internal consistency, within the normal limits of experimental error in these types of measurement. Once E⁰ was determined, the mean ionic activity coefficients of NaBr (γ), the Gibbs energy of transfer of the NaBr from the water to the EC + water mixture (ΔG_t⁰), the standard solubility product of NaBr in EC + water (K_sp0), the NaBr primary hydration number (n _hyd), Gibbs energy interaction parameters (g_EN), and the salting constant (k_S) were estimated. The results were comparatively analyzed with those of NaF and NaCl previously obtained in similar mixtures.