Activity coefficients for NH4Cl in ethanol-water mixed solvents by electromotive force measurements

Pitzer ion-interaction model and electromotive force (emf) data of a galvanic cell without liquid junction were used for the determination of activity coefficients of NH4Cl in different ethanol-water mixed solvents at 25 °C. The used galvanic cell is schematically represented by: Ag∣AgCl∣NH4Cl (m), H2O (100-w%), EtOH (w%)∣NH4+ (ISE), in which ISE stands for ion-selective electrode and w for the mass fraction percent of ethanol. The mixed ethanol-water systems contained, respectively, 0, 10, 20, 30, 40, and 50 mass fraction percent EtOH. The experimental emf data were obtained using a solvent polymeric PVC ammonium selective membrane electrode containing a mixture of nonactin/monactin as ionophore and an Ag/AgCl electrode. Activity coefficients were determined over the molality range from dilute solution to near salt saturation (i.e., about 5.38 mol/kg in pure water or 2 mol/kg in 50% mixed EtOH-water solvent).