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 wat er 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 grou ps are assigned a (V) over bar degrees contribution and the partial mo lar volumes of more than 150 monofunctional organic ions ale reproduce d with a standard deviation of 0.8 cm(3)-mol(-1). The different volume tric behavior of hydrophobic and hydrophilic centers, either charged o r uncharged, is discussed. Deviations from additivity for mono- and po lyfunctional ions are analyzed in terms of (i) extension of the hydrat ion cosphere of different polar centres; (ii) intramolecular interacti ons and their dependence on the nature, number and mutual separation o f interacting groups.