NH4Cl + NH4NO3 + H2O Ternary Mixed Electrolyte System: Thermodynamic Modeling Based on Potentiometric Measurements

Abstract

This work reports the results of the thermodynamic modeling of NH4Cl salt in the ternary NH4Cl (m1) + NH4NO3 (m2) + H2O mixed electrolyte system based on potentiometric measurements. The electrochemical measurements were performed, at similar constant ionic strengths, in different series of mixed salt solutions, each characterized by a fixed salt molal ratio r (where r = m1/m2 = 0.05, 1, 5, 10, and m1, m2 are the molalities of NH4Cl and NH4NO3, respectively). The galvanic cell used for collecting the potentiometric data consisted of a solvent polymeric (PVC) NH4+ selective membrane electrode (NH4+ ISE) and an Ag/AgCl electrode. Pitzer ion-interaction equations for mixed salts were used for modeling the nonideal behavior of the system, over the ionic strength ranging from 0.01 mol·kg−1 up to about 6 mol·kg−1, at 298.15 K. On the basis of the obtained Pitzer ion-interaction parameters, the osmotic coefficients, solvent activities, and excess Gibbs free energies were also determined for these investigated te...