Partial molal volumes and compressibilities of phosphoric acid and sodium phosphates in 0.725 modlal NaCl at 25 °c

Frank J. Millero, Fen Huang, Antonio Lo Surdo, Faina Vinokurova

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The apparent molal volume Vβ and adiabatic compressibility κβ of H3PO4, NaH2PO 4, Na2HPO4, and Na3PO4 have been determined from density and sound speed measurements in 0.725 m NaCl solutions at 25 °C. The partial molal volumes V̄i* and compressibilities κ̄i* have been determined by extrapolating the values of Vβ and κβ to infinite dilution in the NaCl media. The results have been compared to earlier measurements made on a number of electrolytes in NaCl media. The phosphate results showed correlations between the values of V̄i* and κ̄i* as found for other electrolytes. The values for the volume ΔVi and compressibility Δκ i changes for the dissociation of H3PO4 in 0.725 m NaCl have been calculated from the measurements. The calculated values of ΔVi and compressibility Δκi have been used to estimate the effect of pressure KP/K0 on the dissociation of H3PO4 in the oceans using RT ln[K P/K0] = -ΔViP + 0. 5ΔκiP2, where P is the applied pressure in bars. The results are in reasonable agreement with directly measured values.

Original languageEnglish (US)
Pages (from-to)16099-16104
Number of pages6
JournalJournal of Physical Chemistry B
Issue number49
StatePublished - Dec 16 2010


ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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