The dissociation of carbonic acid in NaCl solutions as a function of concentration and temperature

Frank Millero, Fen Huang, Taylor Graham, Denis Pierrot

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74 Scopus citations


Potentiometric measurements of the stoichiometric constants for the dissociation of carbonic acid in NaCl solutions (K1* = [H+] [HCO3-] / [CO2] and K1* = [H+] [CO32 -] / [HCO3-]) have been made as a function of molality (0-6 m) and temperature (0-50 °C). The results have been fitted to the equationsp Ki* - p Ki = Ai + Bi / T + Ci ln TThe values of pKi in pure water are taken from the literature and the adjustable parameters Ai, Bi and Ci are a function of molalityA1 = 35.2911 m0.5 + 0.8491 m - 0.32 m1.5 + 0.055 m2B1 = - 1583.09 m0.5C1 = - 5.4366 m0.5A2 = 38.2746 m0.5 + 1.6057 m - 0.647 m1.5 + 0.113 m2B2 = - 1738.16 m0.5C2 = - 6.0346 m0.5(σ = 0.013 for p K1* and σ = 0.020 for p K2*, N = 603). The values determined in this study are in good agreement with the 25 °C literature values. Our results have been combined with previous measurements to derive equations that are valid from 0 to 250 °C and 0 to 5 m. This large data set has been used to determine the Pitzer parameters (β(0), β(1) and Cφ{symbol}) for the interactions of Na+ with HCO3- and CO32- from 0 to 250 °C. These results extend the carbonate system Pitzer model to hydrothermal brines containing high concentrations of NaCl.

Original languageEnglish (US)
Pages (from-to)46-55
Number of pages10
JournalGeochimica et Cosmochimica Acta
Issue number1
StatePublished - Jan 1 2007

ASJC Scopus subject areas

  • Geochemistry and Petrology


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