Influence du milieu sur les volumes molaires partiels de divers sels

Laboratoire de Physicochimie des Solutions, La CNRS 161, E.N.S.C.P., 11, rue Pierre et Marie Curie, 75231 Paris Cédex 05, France.

Résumé

Les volumes molaires partiels à dilution infinie [Math] de onze halogénures alcalins ou organiques (R₄NBr) ont été déterminés dans l'eau, le diméthylsulfoxyde en huit mélanges de ces solvants, régulièrement répartis sur l’échelle des fractions molaires. Les volumes d’excès des sels minéraux sont correctement décrits par un modèle très simple et celui-ci montre qu’ils découlent essentiellement des volumes molaires partiels des cosolvants dans le système binaire eau-DMSO.

Abstract

The partial molar volume at infinite dilution of 13 salts were determined in pure water, in pure dimethy Isulfoxide (Me₂SO), and in eight mixtures of the two solvents.

The behaviour of the inorganic salts is described by a model involving the volumetric properties of the co-solvents, and two solvation parameters characteristic of the solute. The model indicates the origin of the excess volume to be intimately related to the nonideality of the mixed solvent.

The shapes of the curves, and especially the maxima which appear at X_DMSO close to 0.3, are correctly described by our equations.

The range of use of this model may be extended to provide individual behaviour of ions, by the choice of an appropriate extra-thermodynamical hypothesis.

For organic salts, experimental curves have very different shapes with a sharp minimum at X_DMSO close to 0.15.

The model does not work for organic ions and indicates that their intrinsic volumes may change with the nature of the solvent.