The enthalpies of dilution of phosphate solutions at 30°C

Frank J. Millero, Wayne C. Duer, Elizabeth Shepard, Peter V. Chetirkin

Research output: Contribution to journalArticle

12 Scopus citations

Abstract

The enthalpies of dilution of aqueous solutions of HCl, H3PO4, NaOH, NaH2PO4, Na2HPO4 and Na3PO4 in the molality range 0.1 to 1.0 mole-kg-1 have been determined at 30°C. The relative apparent molal enthalpies φL of HCl, NaOH, NaH2PO4 and Na2HPO4 have been determined with the aid of an extended form of the Debye-Hückel limiting law. The relative apparent molal enthalpies for Na3PO4 solutions have been corrected for hydrolysis. A value of ΔHHo=9525±150 cal-mole-1 was determined for the heat of hydrolysis of PO4-3. This value gives ΔH3o=3815±150 cal-mole-1 for the ionization of H2PO4-, which is in good agreement with the value of ΔH3o=3500±500 cal-mole-1 determined directly by Pitzer at 25°C. The relative apparent molal enthalpies for H3PO4 solutions have been corrected for ionization. A value of ΔH1o=-1900±150 cal-mole-1 was obtained for the heat of ionization of H3PO4 to H++H2PO4-. This value is in good agreement with the value of ΔH1o=-2031 cal-mole-1 at 30°C determined by Harned and Owen from the temperature coefficient of the equilibrium constant and ΔH1o=-1950±80 cal-mole-1 at 25°C determined from calorimetry by Pitzer.

Original languageEnglish (US)
Pages (from-to)877-889
Number of pages13
JournalJournal of Solution Chemistry
Volume7
Issue number12
DOIs
StatePublished - Dec 1 1978

Keywords

  • Ionization of phosphoric acid
  • enthalpy of dilution
  • phosphate solutions

ASJC Scopus subject areas

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

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    Millero, F. J., Duer, W. C., Shepard, E., & Chetirkin, P. V. (1978). The enthalpies of dilution of phosphate solutions at 30°C. Journal of Solution Chemistry, 7(12), 877-889. https://doi.org/10.1007/BF00645297