Potentiometric determination of activity coefficients for NH4Cl in the ternary NH4Cl/LiCl/H2O mixed electrolyte system

This work reports the results of the determination of mean activity coefficients for NH4Cl in ternary (NH4Cl(m1) + LiCl(m2) + H2O) electrolyte system by potentiometric method at 25 °C. The experimental potentiometric data were obtained by combining a solvent polymeric (PVC) ammonium-selective membrane electrode (NH4+ ISE), containing a mixture of nonactin/monactin as ionophore, and an Ag|AgCl electrode. The measurements were performed, at constant ionic strength, in different series of mixed salt solutions characterized by a fixed salt mole ratio r (where r = m1/m2 = 25, 50, 75, 100). The non-ideal behavior of the system was described on the base of the Pitzer ion-interaction model for mixed salts, over the molality ranging from 0.01 to 3 mol/kg.