Volume change for the formation of magnesium sulfate ion pairs at various temperatures

Frank J Millero, William L. Masterton

Research output: Contribution to journalArticle

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Abstract

The apparent molal volumes of aqueous MgSO4 solutions from 0 to 1 m at 0, 25, and 50° have been used to estimate the apparent molal volume of the ion pair MgSO4°, φV(MgSO4°) using the relation φV(obsd) = (1 - α)φV(MgSO4°) + αφV(Mg2+, SO42-) where φV(obsd) is the observed apparent molal volume for MgSO4 solutions at molality mT, α is the fraction of free ions, and φV(Mg2+, SO42-) is the apparent molal volume of the free ions Mg2+ and SO42- at the ionic strength Im = 4αmT. Using known association constants for the formation of MgSO4° and various estimates for φV(Mg2+, SO42-), we have determined the φV of MgSO4° and ΔφV for its formation as a function of temperature and concentration. The infinite dilution values for the φV° of the ion pair MgSO4° appear to be independent of the various estimates of the φV of the free ions Mg2+ + SO42-. The ΔV̄° = ΔφV° for the formation of MgSO4 at 25° is in reasonable agreement with the results calculated from the high-pressure conductance data of Fisher and theoretical estimates. The ΔV̄° calculated from the density data appears to go through a minimum when plotted vs. temperature similar to the volume change for the ionization of weak acids and bases. The φV° and ΔφV° results for MgSO4° are briefly discussed in terms of the structure of the ion pair.

Original languageEnglish (US)
Pages (from-to)1287-1294
Number of pages8
JournalJournal of Physical Chemistry
Volume78
Issue number13
StatePublished - 1974

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magnesium sulfates
Magnesium Sulfate
Magnesium
Ions
ions
estimates
Temperature
temperature
Ionic strength
Dilution
Ionization
dilution
Sulfates
Association reactions
aqueous solutions
ionization
acids
Acids

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Volume change for the formation of magnesium sulfate ion pairs at various temperatures. / Millero, Frank J; Masterton, William L.

In: Journal of Physical Chemistry, Vol. 78, No. 13, 1974, p. 1287-1294.

Research output: Contribution to journalArticle

Millero, Frank J ; Masterton, William L. / Volume change for the formation of magnesium sulfate ion pairs at various temperatures. In: Journal of Physical Chemistry. 1974 ; Vol. 78, No. 13. pp. 1287-1294.
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abstract = "The apparent molal volumes of aqueous MgSO4 solutions from 0 to 1 m at 0, 25, and 50° have been used to estimate the apparent molal volume of the ion pair MgSO4°, φV(MgSO4°) using the relation φV(obsd) = (1 - α)φV(MgSO4°) + αφV(Mg2+, SO42-) where φV(obsd) is the observed apparent molal volume for MgSO4 solutions at molality mT, α is the fraction of free ions, and φV(Mg2+, SO42-) is the apparent molal volume of the free ions Mg2+ and SO42- at the ionic strength Im = 4αmT. Using known association constants for the formation of MgSO4° and various estimates for φV(Mg2+, SO42-), we have determined the φV of MgSO4° and ΔφV for its formation as a function of temperature and concentration. The infinite dilution values for the φV° of the ion pair MgSO4° appear to be independent of the various estimates of the φV of the free ions Mg2+ + SO42-. The ΔV̄° = ΔφV° for the formation of MgSO4 at 25° is in reasonable agreement with the results calculated from the high-pressure conductance data of Fisher and theoretical estimates. The ΔV̄° calculated from the density data appears to go through a minimum when plotted vs. temperature similar to the volume change for the ionization of weak acids and bases. The φV° and ΔφV° results for MgSO4° are briefly discussed in terms of the structure of the ion pair.",
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N2 - The apparent molal volumes of aqueous MgSO4 solutions from 0 to 1 m at 0, 25, and 50° have been used to estimate the apparent molal volume of the ion pair MgSO4°, φV(MgSO4°) using the relation φV(obsd) = (1 - α)φV(MgSO4°) + αφV(Mg2+, SO42-) where φV(obsd) is the observed apparent molal volume for MgSO4 solutions at molality mT, α is the fraction of free ions, and φV(Mg2+, SO42-) is the apparent molal volume of the free ions Mg2+ and SO42- at the ionic strength Im = 4αmT. Using known association constants for the formation of MgSO4° and various estimates for φV(Mg2+, SO42-), we have determined the φV of MgSO4° and ΔφV for its formation as a function of temperature and concentration. The infinite dilution values for the φV° of the ion pair MgSO4° appear to be independent of the various estimates of the φV of the free ions Mg2+ + SO42-. The ΔV̄° = ΔφV° for the formation of MgSO4 at 25° is in reasonable agreement with the results calculated from the high-pressure conductance data of Fisher and theoretical estimates. The ΔV̄° calculated from the density data appears to go through a minimum when plotted vs. temperature similar to the volume change for the ionization of weak acids and bases. The φV° and ΔφV° results for MgSO4° are briefly discussed in terms of the structure of the ion pair.

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