The ionization of boric acid in NaCl, NaCaCl and NaMgCl solutions at 25°C

J. Peter Hershey, Marino Fernandez, Peter J. Milne, Frank J. Millero

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91 Scopus citations


The stoichiometric pK{black star} for the ionization of boric acid has been determined from emf measurements in pure NaCl solution and in NaCl solution with small amounts of added CaCl2 and MgCl2 from I = 0.5 to 6.0 molal at 25°C. Our results in NaCl media at low concentrations are in good agreement (±0.01 pK units) with the results of Owen and King (1943). From the values of the pK{black star} we have determined the Pitzer parameters β0, β1 and Cø for the interactions of Ca2+ and Mg2+ with B(OH)4-. Ion pairing constants for the interaction of borate ion with Ca2+ and Mg2+ were also determined from I = 0.5 to 6 m and values were extrapolated to pure water. These interactions are weak and the pK's in water and in NaCl solution are in reasonable agreement with values of other workers. Pitzer terms (β[MA]Cl0) for the interaction of [MA] ion pairs with Cl- were also determined. The pKHA{black star} data can be fitted within experimental error with one less parameter using the combined ion pairing/Pitzer approach than when using the Pitzer formalism alone. We, thus, favor the combined approach for calculating the ionic interactions in these solutions.

Original languageEnglish (US)
Pages (from-to)143-148
Number of pages6
JournalGeochimica et Cosmochimica Acta
Issue number1
StatePublished - Jan 1986

ASJC Scopus subject areas

  • Geochemistry and Petrology


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