Development of a Thermodynamic Model Using a Speciation Framework: Illustration on the HNO<inf>3</inf>-H<inf>2</inf>O System

A rigorous thermodynamic framework based on speciation analysis is developed for an aqueous solution of nitric acid in this work. The model uses experimentally measured "extent of dissociation" for determining the thermodynamic dissociation constant of nitric acid in aqueous solutions at 25 °C. The activity coefficients of H+ and NO3- ions are modeled using Specific Ion Interaction Theory (SIT). SIT parameters for H+ and NO3- ionic activity coefficients and the parameters for activity coefficient of undissociated HNO3 are obtained using the proposed methodology. An important contribution of our approach is that the model developed is applicable over the concentration range of 0-22 M nitric acid which is of practical relevance. The model predictions of concentrations are consistent with data reported in the literature.