Sound speed and density measurements for tetra-n-butylammonium bromide in benzene and carbon tetrachloride solutions at T = 298.15 K

The density and sound speed measurements have been carried out for the binary systems consisting of tetra-n-butylammonium bromide (Bu4NBr) as a solute in benzene and CCl4 at T = 298.15 K (concentration range 0.01 mol · kg−1 to ∼0.8  mol · kg−1). The apparent molar volumes (ϕV) and apparent molar isentropic compressibility (ϕKS)(ϕKS) have been calculated and the values at infinite dilution are estimated. These data for Bu4NBr in benzene and CCl4 solutions are combined with the literature data of Bu4NBr in water to obtain transfer compressibility of Bu4NBr molecules from non-aqueous to aqueous solutions. The ϕV behaviour as a function of concentration in benzene solutions indicates formation of reverse micelles and having critical micelle concentration (cmc) around 0.01x2 of Bu4NBr (∼0.13 mol · kg−1). The compressibility data are further used to estimate hydration number of Bu4NBr in aqueous solutions by applying Shiio’s method. The hydration number calculated for compressible organic electrolyte shows good agreement with the number obtained for clathrate hydrate of Bu4NBr using the chemical analysis and X-ray diffraction.