Effect of ionic strength and ionic interactions on the oxidation of Fe(II)

Frank J. Millero, Miguel Izaguirre

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59 Scopus citations


The rates of oxidation of Fe(II) in NaCl and NaClO4 solutions were studied as a function of pH (6 to 9), temperature (5 to 25°C), and ionic strength (0 to 6m). The rates are second order with respect to [H+] or [OH-] and independent of ionic strength and temperature. The overall rate of the oxidation is given by {Mathematical expression} where [OH-]=KW*/[H+](KW* is the stoichiometric dissociation constant for water) and [O2] is the molal concentration of the oxygen. The experimental results were fitted to equations of the form {Mathematical expression} where log k0=21.56-1545/T, A=0.470, B=-646, and C=0.723 (σ=0.07) for NaCl; A=-1.638, B=0, and C=0.836 (σ=0.11) for NaClO4. The lower results in NaCl at higher ionic strengths are attributed to the formation of FeCl+ that has a slower rate of oxidation. The kinetic results give βFeCl = 1.2 ± 0.5, which is in reasonable agreement with literature data. Measurements of the effect of various ions on the rates were studied at constant ionic strength. The results were in the order HCO3->Br->ClO4->Cl->NO3->SO42->B(OH)4- and were attributed to the relative strength of the interactions of Fe2+ with these anions. The strong interactions of Fe2+ with SO42- and B(OH)4- were used to estimate the stability constants, log βFeSO4 = 1.8 ± 0.1 and log βFeB(OH)4 = 3.2 ± 0.1, which are in reasonable agreement with literature data.

Original languageEnglish (US)
Pages (from-to)585-599
Number of pages15
JournalJournal of Solution Chemistry
Issue number6
StatePublished - Jun 1 1989


  • Fe(II)
  • NaCl
  • NaClO
  • ionic strength
  • oxidation

ASJC Scopus subject areas

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


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