Thermodynamic studies of ionic interactions in aqueous solutions of N-butyl-pyridinium bromide at 298.15Â K

Density and osmotic coefficient measurements for aqueous solutions of N-butyl-pyridinium bromide [Bpy][Br] in concentration range ~ 0.019 to ~ 0.39 mol·kg− 1 at 298.15 K are reported. The density data are used to obtain apparent molar volume (ϕV), partial molar volume of solute and solvent V¯2andV¯1 respectively as well the limiting partial molar volume ϕ¯V0=V¯20 of the solute [Bpy][Br] (by appropriate extrapolation). The experimental osmotic coefficient (ϕ) data are used to determine the activity and mean ionic activity coefficients of solute and solvent respectively. Experimental activity coefficient data are compared with those obtained from Debye-Hückel and Pitzer models. The activity data have been further processed to obtain the Gibbs free energy change due to mixing (ΔGm) and excess Gibbs free energy change (ΔGE). The aggregation number (n) and critical micelle concentration (cmc) are obtained for ionic salt in solution phase by applying pseudo-phase separation model to ϕ and ϕV data respectively. Application of McMillan-Mayer theory of solutions to the data is made. The results have been interpreted on the basis of structural characteristic of salt, ion-solvent and ion-ion interactions.