Dissociation Constants of Ammonium Ion and Activity Coefficients of Ammonia in Ammonium Nitrate Solutions

Abstract

Dissociation constants of NH 4 + ion on the molality basis (K a,m =[H + ][NH 3 ][NH 4 + ]) were determined at 298.15 K in aqueous NH 4 NO 3 solutions at different ionic strengths (I=0.5-10.8 mol.kg -1 ) by means of a glass electrode. The pK a,m values increase gradually with increasing ionic strength. The activity coefficients of NH 3 , γ m,NH3 on the molality basis in the NH 4 NO 3 solutions were determined by a transpiration method and were fitted to ln γ m,NH3 =-0.0416I m +0.001941 m2 (I=0.5-10.8 mol.kg -1 ). The observed dissociation constants, pK a,m , were compared with those calculated from the Pitzer equations