Group contributions to the partial molar volume of ionic organic solutes in aqueous solution

Partial molar volumes at infintie dilution (V) over bar degrees in water at 25 degrees C for more than 400 organic electrolytes (carboxylic acid and amine salts, sulfates, sulfonates, selected polyelectrolytes, aminoacids and derivatives) are described through a simple additivity scheme already adopted for non-electrolytes. Twenty-five charged groups are assigned a (V) over bar degrees contribution and the partial molar volumes of more than 150 monofunctional organic ions ale reproduced with a standard deviation of 0.8 cm(3)-mol(-1). The different volumetric behavior of hydrophobic and hydrophilic centers, either charged or uncharged, is discussed. Deviations from additivity for mono- and polyfunctional ions are analyzed in terms of (i) extension of the hydration cosphere of different polar centres; (ii) intramolecular interactions and their dependence on the nature, number and mutual separation of interacting groups.