Dissociation constants of carbonic acid in seawater as a function of salinity and temperature

Frank J. Millero, Taylor B. Graham, Fen Huang, Héctor Bustos-Serrano, Denis Pierrot

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Abstract

Potentiometric measurements of the stoichiometric constants on the seawater pH scale for the dissociation of carbonic acid in seawater (K1* = [H+][HCO3-]/[CO2] and K2* = [H+][CO32-]/[HCO3-]) have been made as a function of salinity (1 to 50) and temperature (0 to 50 °C). The results have been fitted to the equations (T/K){A formula is presented}. The values of pKi0 in pure water are taken from the early work of Harned and Davis (1943) and Harned and Scholes (1941){A formula is presented}{A formula is presented}. The value of the adjustable parameters Ai, Bi and Ci for pK1* are given by (σ = 0.0054 and N = 466){A formula is presented}{A formula is presented}{A formula is presented}. For pK2* the parameters are given by (σ = 0.011 and N = 458){A formula is presented}{A formula is presented}{A formula is presented}. The values of pK1* and pK2* determined in this study are in good agreement with the seawater (SW) measurements of Mehrbach et al. (1973) and Mojica-Prieto and Millero (2002) from S = 15 to 45 and 0 to 40 °C. The values of pK1* near S = 35 are also in reasonable agreement with the measurements in artificial seawater (ASW) of Goyet and Poisson (1989) and Roy et al. (1993) from 0 to 35 °C. The values of pK2* in real seawater, however, do not agree with the measurement made in artificial seawater at temperatures above 5 °C. Calculations of pK1* and pK2* near 25 °C using an ionic interaction model (Millero and Roy, 1997) suggest that the pK2* results in SW are more reliable than in ASW. The equations from this study should be valid from S = 0 to 50 and t = 0 to 50 °C for most estuarine and marine waters (check values at S = 35 and t = 25 °C are pK1* = 5.8401 and pK2* = 8.9636).

Original languageEnglish (US)
Pages (from-to)80-94
Number of pages15
JournalMarine Chemistry
Volume100
Issue number1-2
DOIs
StatePublished - Jun 1 2006

Keywords

  • Carbonic acid
  • Dissociation constants
  • Modeling
  • Seawater
  • Titration
  • pK
  • pK

ASJC Scopus subject areas

  • Oceanography
  • Chemistry(all)
  • Environmental Chemistry
  • Water Science and Technology

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    Millero, F. J., Graham, T. B., Huang, F., Bustos-Serrano, H., & Pierrot, D. (2006). Dissociation constants of carbonic acid in seawater as a function of salinity and temperature. Marine Chemistry, 100(1-2), 80-94. https://doi.org/10.1016/j.marchem.2005.12.001