### 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) |
---|---|

Pages (from-to) | 269-280 |

Number of pages | 12 |

Journal | Journal of Solution Chemistry |

Volume | 6 |

Issue number | 4 |

DOIs | |

State | Published - Apr 1977 |

### Fingerprint

### Keywords

- Calcium sulfate
- ion pair
- molal volume and compressibility

### ASJC Scopus subject areas

- Physical and Theoretical Chemistry

### Cite this

*Journal of Solution Chemistry*,

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

**The partial molal volume and compressibility change for the formation of the calcium sulfate ion pair at 25°C.** / Millero, Frank J; Gombar, Francis; Oster, Jeffrey.

Research output: Contribution to journal › Article

*Journal of Solution Chemistry*, vol. 6, no. 4, pp. 269-280. https://doi.org/10.1007/BF00645458

}

TY - JOUR

T1 - The partial molal volume and compressibility change for the formation of the calcium sulfate ion pair at 25°C

AU - Millero, Frank J

AU - Gombar, Francis

AU - Oster, Jeffrey

PY - 1977/4

Y1 - 1977/4

N2 - The apparent molal volumes (φv) and compressibilities (φK) of CaSO4 solutions have been determined at 25°C from precise density and sound-speed measurements. The large deviations of the values of φv and φK from the limiting law and various additivity estimates for the free ions (Ca2+, SO4 2-) have been used to estimate the partial molal volume ( {Mathematical expression}) and compressibility ( {Mathematical expression}) for the formation of the CaSO4 0 ion pair. Values of {Mathematical expression}= 25 ± 3 cm3-mole-1 and {Mathematical expression}= (54±21)×10-4 cm3-mole-1-bar-1 were found. Since these values are larger than the value for the formation of MgSO4 0, the results indicate that more inner-sphere ion pairs are formed when SO4 2- complexes with Ca2+ than with Mg2+. Using a simple model for ion-water interactions, the percent of inner-sphere or contact ion pairs in CaSO4 solutions is estimated to be 36 to 37%.

AB - The apparent molal volumes (φv) and compressibilities (φK) of CaSO4 solutions have been determined at 25°C from precise density and sound-speed measurements. The large deviations of the values of φv and φK from the limiting law and various additivity estimates for the free ions (Ca2+, SO4 2-) have been used to estimate the partial molal volume ( {Mathematical expression}) and compressibility ( {Mathematical expression}) for the formation of the CaSO4 0 ion pair. Values of {Mathematical expression}= 25 ± 3 cm3-mole-1 and {Mathematical expression}= (54±21)×10-4 cm3-mole-1-bar-1 were found. Since these values are larger than the value for the formation of MgSO4 0, the results indicate that more inner-sphere ion pairs are formed when SO4 2- complexes with Ca2+ than with Mg2+. Using a simple model for ion-water interactions, the percent of inner-sphere or contact ion pairs in CaSO4 solutions is estimated to be 36 to 37%.

KW - Calcium sulfate

KW - ion pair

KW - molal volume and compressibility

UR - http://www.scopus.com/inward/record.url?scp=0009105933&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0009105933&partnerID=8YFLogxK

U2 - 10.1007/BF00645458

DO - 10.1007/BF00645458

M3 - Article

VL - 6

SP - 269

EP - 280

JO - Journal of Solution Chemistry

JF - Journal of Solution Chemistry

SN - 0095-9782

IS - 4

ER -