Effect of temperature on the partial molar volumes of some high valency electrolytes in water-rich region of binary aqueo-organic mixtures

Abstract

Partial molar volumes of some high valency electrolytes viz. potassium ferrocyanide and potassium ferricyanide have been determined in aqueous and binary aqueo-organic mixtures of acetonitrile (ACN) and methanol (MeOH) in water-rich region [5, 10, 15, 20 and 25% by weight of ACN and MeOH] from solution density measurements at 303.15 K, and in water and 5% (w/w) ACN + H 2 O and MeOH + H 2 O at five equidistant temperatures [298.15, 303.15, 308.15, 313.15 and 318.15 K]. The density data have been analysed by means of Masson's equation. The partial molar volumes (φ 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 capacities of the high valency electrolytes have been inferred from the sign of [ 2 φ 0 v /T 2 ] p i.e. the second derivative of partial molar volumes w.r.t. temperature at constant pressure. The high valency electrolytes behave like common electrolytes in water and like symmetrical tetra-alkyl ammonium salts in binary aqueo-organic mixtures. The high valency electrolytes act as structure breakers in water and structure makers in binary aqueo-organic mixtures. The behaviour of high valency electrolytes changes on the addition of organic solvent.