## Abstract

The isothermal compressibilities (β's) of aqueous NaCl, Na_{2}SO_{4}, MgSO_{4}, and MgCl_{2} solutions have been measured at 0, 15, 30, and 45° by a piezometric technique. The compressibilities were determined at applied pressures P = 8.7, 16.8, and 25.7 bars and the data were extrapolated to 1 atm. The β's have been fitted to an equation of the form, β = β^{0}+ A_{K}c + B_{K}c^{3/2}, where β^{0} is the compressibility of pure water, c is the molar concentration, and A_{K} and B_{K} are temperature-dependent parameters. The equation fits the compressibility data to ±0.07 × 10^{-6} bar^{-1} for all the salts. The apparent molal compressibilities, φ_{K}, have been calculated from the compressibility data. At high concentrations the concentration dependence of the (φ_{K})'s were found to follow the equation, φ_{K} = φ_{K}^{0} + S_{K}*I_{V}^{1/2}, where φ_{K}^{0} and S_{K}* are empirical constants and I_{V} is the molar ionic strength. To obtain reliable infinite dilution (φ_{K}^{0})'s (that agree with values derived from sound velocity measurements) it was necessary to use the equation, φ_{K} = φ_{K}^{0} + S_{K}I_{V}^{1/2} + b_{K}I_{V}, where φ_{K}^{0} is the infinite dilution apparent molal compressibility, S_{K} is the Debye-Hückel limiting law slope, and b_{K} is a temperature-dependent parameter related to deviations from the limiting law. The (φ_{K}^{0})'s from all the electrolytes increase with increasing temperature and appear to go through a maximum between 40 and 50°. The deviations from the limiting law, b_{K}, are all positive at low temperature and decrease with increasing temperatures for all the salts. The (φ_{K})'s are briefly discussed in terms of the ion-water and ion-ion interactions responsible for the observed behavior The (φ_{K})'s for MgSO_{4} solutions have been analyzed by assuming the ion pair, MgSO_{4}^{0}, is formed. The Δφ^{K} for the formation of the ion pair and the φ_{K} of MgSO_{4}^{0} have been calculated at various concentrations and temperatures. The results are used to examine the structure of the ion pair.

Original language | English (US) |
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Pages (from-to) | 1636-1643 |

Number of pages | 8 |

Journal | Journal of physical chemistry |

Volume | 78 |

Issue number | 16 |

DOIs | |

State | Published - 1974 |

## ASJC Scopus subject areas

- Engineering(all)
- Physical and Theoretical Chemistry