### Abstract

The apparent molal volumes (φ_{v}) and compressibilities (φ_{K}) of CaSO_{4} solutions have been determined at 25°C from precise density and sound-speed measurements. The large deviations of the values of φ_{v} and φ_{K} from the limiting law and various additivity estimates for the free ions (Ca^{2+}, SO_{4}^{2-}) have been used to estimate the partial molal volume ( {Mathematical expression}) and compressibility ( {Mathematical expression}) for the formation of the CaSO_{4}^{0} ion pair. Values of {Mathematical expression}= 25 ± 3 cm^{3}-mole^{-1} and {Mathematical expression}= (54±21)×10^{-4} cm^{3}-mole^{-1}-bar^{-1} were found. Since these values are larger than the value for the formation of MgSO_{4}^{0}, the results indicate that more inner-sphere ion pairs are formed when SO_{4}^{2-} complexes with Ca^{2+} than with Mg^{2+}. Using a simple model for ion-water interactions, the percent of inner-sphere or contact ion pairs in CaSO_{4} solutions is estimated to be 36 to 37%.

Original language | English (US) |
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Pages (from-to) | 269-280 |

Number of pages | 12 |

Journal | Journal of Solution Chemistry |

Volume | 6 |

Issue number | 4 |

DOIs | |

State | Published - Apr 1 1977 |

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### Keywords

- Calcium sulfate
- ion pair
- molal volume and compressibility

### ASJC Scopus subject areas

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

### Cite this

*Journal of Solution Chemistry*,

*6*(4), 269-280. https://doi.org/10.1007/BF00645458