Determination of activity coefficients for NH4Cl in 1-propanol/water mixed solvents by potentiometric measurements

Activity coefficients for NH4Cl in different 1-propanol/water mixed solvents were determined at 25 °C using experimental electromotive force (emf) data of the following galvanic cell: Ag|AgCl|NH4Cl(m),H2O(100−w%),1−PrOH(w%)|NH4+(ISE), in which ISE stands for the ion-selective electrode and w for the mass fraction percent of 1-propanol. The measurements were performed in various mixed 1-propanol/H2O solvent systems containing 0, 10, 20, 30, 40 and 50 mass fraction percent of 1-propanol, respectively. The experimental emf data were obtained by a solvent polymeric PVC ammonium-selective membrane electrode containing a mixture of nonactin/monactin as ionophore and an Ag/AgCl electrode. The non-ideal behavior of the electrolyte system was described, for each mixed solvent system, on the base of the Pitzer ion-interaction model by determining the related coefficients over the molality range from dilute solution to near salt saturation (i.e. about 5.13 mol/kg in pure water or 2.34 mol/kg in 50% mixed 1-propanol/water solvent).