Activity coefficients for NH 4Cl in ethanol–water mixed solvents by electromotive force measurements

Abstract

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 NH 4Cl in different ethanol–water mixed solvents at 25 °C. The used galvanic cell is schematically represented by: Ag∣AgCl∣NH 4Cl (m), H 2O (100-w%), EtOH (w%)∣NH 4 + (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).