## 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) |
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Pages (from-to) | 1287-1294 |

Number of pages | 8 |

Journal | Journal of physical chemistry |

Volume | 78 |

Issue number | 13 |

DOIs | |

State | Published - Jan 1 1974 |

## ASJC Scopus subject areas

- Engineering(all)
- Physical and Theoretical Chemistry