H2O-D2O solvent isotope effects in the volume and expansivity behaviour of some organic and inorganic ions

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Abstract
Changes of structure of the water solvent caused by organic and inorganic ions have been investigated by measurements of the H2O-D2O solvent isotope effect in the partial molar volumes text-decoration:overlineV 2 of alkali halides, tetraalkylammonium (TAA) and other ammonium type salts over a range of temperatures. The structure promoting hydrophobic ions have larger text-decoration:overlineV 2 in D2O than in H2O, while the more electrostricting simple inorganic ions have smaller volumes in D2O than in H2O. By means of an extrapolation procedure based on the additivity of text-decoration:overlineV°2 for homologous TAA salts, the individual ionic contributions to the solvent isotopic volume difference can be evaluated. On this basis, the results indicate that the anions are predominantly the species that are associated with the so-called structure breaking effects in the simple salt solutions while K+ and the TAA cations exhibit an opposite kind of behaviour . The solvent isotope effect in text-decoration:overlineV 2 for pyridine and H (as HOD) is also evaluated. Studies over a range of temperature enabled the partial molal expansibilities to be evaluated in H2O and D2O.

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