The ionization of carbonic acid in Na-Mg-Cl solutions at 25°C

Frank J. Millero, Valerie Thurmond

Research output: Contribution to journalArticlepeer-review

36 Scopus citations


The stoichiometric pK2* and pK2* for the ionization of carbonic acid has been determined from emf measurements in NaCl solutions with small amounts of MgCl2 from I=0.5 to 6.0 molal at 25°C. Our results at low ionic strengths (I=0.7) are in agreement with the measurements of Dyrssen and Hansson and Pytkowicz and Hawley. Our results have been analyzed using the ion pairing model and Pitzer's specific interaction equations. From the values of pK1*, we have determined the Pitzer parameters β0[Mg (HCO3)2] = 0.0193 and β1[Mg (HCO3)2] = 0.0193 which reproduces the pK1* results to ±0.01. The values of pK2* were used to determine β0(MgCO3) = 2.833, β1(MgCO3) = -15.069, β2(MgCO3) = -204.90 and Cφ{symbol} (MgCO3)=-0.970 which reproduces the pK2*′ s to ±0.02. The pK2* results could be reproduced to the same precision with fewer parameters using the ion pairing model [pK(MgCO3)=3.00 and log γ (MgCO3)=0.0560 I].

Original languageEnglish (US)
Pages (from-to)401-412
Number of pages12
JournalJournal of Solution Chemistry
Issue number6
StatePublished - Jun 1 1983


  • Carbonic acid
  • Pitzer parameters
  • ionization
  • weak acids

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Physical and Theoretical Chemistry


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