A comparative study of partial molar volumes of some common, tetra-alkyl ammonium and multivalent electrolytes in aqueous and binary aqueous solutions of urea

The partial molar volumes of some common, tetra-alkyl ammonium and multivalent electrolytes viz., potassium nitrate, ammonium sulphate, tetra-butyl ammonium bromide, tetra-butyl ammonium iodide, ammonium nickel sulphate, ammonium aluminium sulphate, potassium aluminium sulphate and ammonium ceric nitrate have been determined in aqueous and binary aqueous solutions of urea (5, 10, 15, 20 and 25 wt.% of urea) from solution density measurements at 298 K, in water and in 5% (w/w) urea + water at four different temperatures. The density data have been analysed by means of Masson's equation. The partial molar volumes (phi(0)(v)) and slopes (S-v*) have been interpreted in terms of ion-solvent and ion-ion interactions, respectively. The partial molar volumes vary with temperature as a power series of temperature. Structure making/breaking of capacities of the various electrolytes have been inferred from the sign of [partial derivative(2)phi(0)(v)/partial derivative T-2](p), i.e., the second derivative of partial molar volume with respect to temperature at constant pressure. The multivalent electrolytes behave like the symmetrical tetra-alkyl salts but not like common electrolytes in binary aqueous solutions of urea. The multivalent electrolytes and tetra-alkyl salts act as structure makers/promoters, while the common electrolytes act as structure breakers in urea + water solution. (c) 2007 Elsevier B.V. All rights reserved.