Development of a modified Bromley methodology for the estimation of ionic media effects on solution equilibria: Part 6. The chemical model of phosphoric acid in aqueous solution at 25 °C and comparison with arsenic acid

The stoichiometric formation constant values of phosphoric acid, collected from the literature in different ionic media at 25 °C, were used to evaluate the interaction parameters of all the species involved in each equilibrium according to the modified Bromley methodology. These parameters yielded values of the corresponding thermodynamic formation constants (log K10=12.31±0.03, log K20=7.17±0.04, log K30=2.15±0.05). The extension of the basic chemical model for P(V) in natural waters was performed by comparison with the chemical model for As(V). The ionic radii for all the species were calculated and the ionic interaction parameters of all the anions with the main cations in natural waters (Ca2+, Mg2+ and Sr2+) were also predicted.