The apparent molal volume and compressibility of seawater fit to the Pitzer equations

Denis Pierrot, Frank J. Millero

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29 Scopus citations


The density and compressibility of seawater salt solutions for ionic strengths 0 to 0.8 m, temperatures 0-40°C, and applied pressure 0 to 1000 bar are fitted to the Pitzer equations. The apparent molal volumes and compressibilities (Xφ) are fitted to equations of the form Xφ = X̄0 + AXII(1.2 m) In(I + 1.2 I0.5) + 2 RT m(β(0)X + β(1)Xg(y) + m CX) where I is the ionic strength, m is the molality of sea salt, AX is the Debye-Hückel slope for the volume (X = V) or compressibility (X = κ) and g(y) = (2/y2) [1 - (1 + y)exp(x)] where y = 2 I0.5. The Pitzer parameters β(0)X, β(1)X, and CX are fitted to functions of temperature and pressure in the form YX = Σi Σj aij(T - TR)ipj where aij are adjustable parameters, YX is the Pitzer parameter, T is the temperature in K, TR = 298.15 K, and P is the applied pressure in bars (P = 0 at 1 atm or 1.013 bar). The standard deviations of the seawater fits are 8.3×10-6 cm3-g-1 for the specific volumes, 0.0007×10-6 bar-1 for the compressibilities, and 0.63×10-6 K-1 for the thermal expansibilities. At 25°C, the measured densities of seawater are compared to the calculated values using Pitzer coefficients for the major sea salts. The results agree with the measured values to within 45 ×10-6 g-cm-3.

Original languageEnglish (US)
Pages (from-to)719-742
Number of pages24
JournalJournal of Solution Chemistry
Issue number8
StatePublished - Aug 2000


  • Apparent molal volumes
  • Apparent molar compressibilities
  • Pitzer equations
  • Sea salts
  • Seawater

ASJC Scopus subject areas

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


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