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, HPO2−4, H3AsO4, H2AsO−4 and HAsO2−4 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.

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