### Abstract

The apparent molal volumes of aqueous MgSO_{4} solutions from 0 to 1 m at 0, 25, and 50° have been used to estimate the apparent molal volume of the ion pair MgSO_{4}°, φ_{V}(MgSO_{4}°) using the relation φ_{V}(obsd) = (1 - α)φ_{V}(MgSO_{4}°) + αφ_{V}(Mg^{2+}, SO_{4}^{2-}) where φ_{V}(obsd) is the observed apparent molal volume for MgSO_{4} solutions at molality m_{T}, α is the fraction of free ions, and φ_{V}(Mg^{2+}, SO_{4}^{2-}) is the apparent molal volume of the free ions Mg^{2+} and SO_{4}^{2-} at the ionic strength I_{m} = 4αm_{T}. Using known association constants for the formation of MgSO_{4}° and various estimates for φ_{V}(Mg^{2+}, SO_{4}^{2-}), we have determined the φ_{V} of MgSO_{4}° and Δφ_{V} for its formation as a function of temperature and concentration. The infinite dilution values for the φ_{V}° of the ion pair MgSO_{4}° appear to be independent of the various estimates of the φ_{V} of the free ions Mg^{2+} + SO_{4}^{2-}. The ΔV̄° = Δφ_{V}° for the formation of MgSO_{4} 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 φ_{V}° and Δφ_{V}° results for MgSO_{4}° are briefly discussed in terms of the structure of the ion pair.

Original language | English (US) |
---|---|

Pages (from-to) | 1287-1294 |

Number of pages | 8 |

Journal | Journal of Physical Chemistry |

Volume | 78 |

Issue number | 13 |

State | Published - 1974 |

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### ASJC Scopus subject areas

- Physical and Theoretical Chemistry

### Cite this

*Journal of Physical Chemistry*,

*78*(13), 1287-1294.

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

Research output: Contribution to journal › Article

*Journal of Physical Chemistry*, vol. 78, no. 13, pp. 1287-1294.

}

TY - JOUR

T1 - Volume change for the formation of magnesium sulfate ion pairs at various temperatures

AU - Millero, Frank J

AU - Masterton, William L.

PY - 1974

Y1 - 1974

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.

AB - 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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M3 - Article

AN - SCOPUS:0009101436

VL - 78

SP - 1287

EP - 1294

JO - Journal of Physical Chemistry

JF - Journal of Physical Chemistry

SN - 0022-3654

IS - 13

ER -