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

Rabindra N. Roy, Jia Zhong Zhang, Frank J. Millero

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


The stoichiometric pK1* and pK2* for the ionization of sulfurous acid has been determined from emf measurements in NaCl solutions with varying concentrations of added MgCl2 (m=0.1, 0.2 and 0.3) from I=0.5 to 6.0 molal at 25°C. These experimental results have been treated using both the ion pairing and Pitzer's specific ion-interaction models. The Pitzer parameters for the interaction of Mg2+ with SO2 and HSO3- yielded λ=0.085±0.004, β(0) = 0.35±0.02, β(1) = 1.2±0.04, and Cφ = -0.072±0.007. The Pitzer parameters β(0) = -2.8±0.4, β(1) = 12.9±2.9 and β(2) = -2071±57 have been determined for the interactions of Mg2+ with SO32-. The calculated values of pK1* and pK2* using Pitzer's equations reproduce the measured values to within ±0.04 pK units. The ion pairing model with log KMgSO3=2.36±0.02 and logγMgSO3 = 0.1021, reproduces the experimental values of pK2* to ±0.01. These results demonstrate that treating the data by considering the formation of MgSO3 yields a better fit of the experimental measurements with fewer adjustable parameters. With these derived coefficients obtained from the Pitzer equations and the ion pairing model, it is possible to make reliable estimates of the activity coefficients of HSO3- and SO32- in seawater, brines and marine aerosols containing Mg2+ ions.

Original languageEnglish (US)
Pages (from-to)361-373
Number of pages13
JournalJournal of Solution Chemistry
Issue number4
StatePublished - Apr 1 1991


  • Ionization
  • NaMgCl
  • Pitzer equations
  • SO
  • activity coefficient
  • ion pairing
  • solubility
  • sulfurous acid

ASJC Scopus subject areas

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


Dive into the research topics of 'The ionization of sulfurous acid in Na-Mg-Cl solutions at 25°C'. Together they form a unique fingerprint.

Cite this