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The dissociation reaction of the bisulfate ion, HSO 4 - ⇌ SO 4 2- + H +, is investigated in aqueous H 2 SO 4 solutions with concentrations of 0.54−15.23 mol kg -1 in the temperature range of 180−326 K using Raman spectroscopy. All investigated H 2 SO 4 solutions show a continuous increase in the degree of dissociation of HSO 4 - with decreasing temperature, in contrast to predictions from thermodynamic models of aqueous H 2 SO 4 solutions. A Pitzer ion interaction model is used to derive a thermodynamically consistent formulation of the thermodynamic dissociation constant of the bisulfate ion, K II ( T ), that is in agreement with the experimental data. The new formulation of K II ( T ) is valid from 180 to 473 K. All ion interaction parameters and the corresponding parametrizations of the Pitzer ion interaction model are presented. Calculations with this model reveal significant differences in ion activity coefficients, water activities, water vapor pressure, and HCl solubilities, when compared to existing thermodynamic models of H 2 SO 4 /H 2 O solutions, in particular at lower temperatures.
Knopf et al. (Sat,) studied this question.