The estimation of the pK^*_HA of acids in seawater using the Pitzer equations

The equations of Pitzer have been used to calculate the stoichiometric ionization constants, pK^*_HA, for acids in NaCl media at 25°C. The calculated results for the ionization of HAc, H₂O, B(OH)₃, H₂CO^-₃, H₃PO₄, H₂PO^-₄, HPO^2-₄, H₃AsO₄, H₂AsO^-₄ and HAsO^2-₄ are in good agreement with the measured values, providing higher order interaction terms (θ and ψ) are used. The pK^*_HA measurements of these acids in NaCl media containing Mg²⁺ and Ca²⁺ were used to determine Pitzer specific interaction parameters at I = 0.7. With these Pitzer coefficients, it was possible to make reliable estimates for the activity coefficients of anions in seawater (S = 35) that form strong interactions with Mg²⁺ and Ca²⁺. The calculated activity coefficients yield reliable estimates for the pK^*_HA of acids in seawater.