Sound speed and density measurements for tetra-n-butylammonium bromide in benzene and carbon tetrachloride solutions at T = 298.15 K
Introduction
Recent studies from our laboratory have been concerned with the thermodynamic properties in binary aqueous and non-aqueous solutions involving 18-crown-6 as a solute. The studies enabled us to understand the solute–solvent interactions, solute–solute hydrophobic interactions, and effects due to conformational changes in solute [1], [2], [3], [4], [5]. Over many years interactions in aqueous solutions have been studied in great detail. The concept of structure making or braking is very popular, since water is highly structured solvent and is the sole medium of life processes. In this context tetra-alkyl ammonium halides have proved to be good model compounds [6], [7], [8], [9], [10], [11], [12], [13], [14]. Among these Bu4NBr form clathrate hydrates (water as a host and Bu4NBr as a guest) [15] and it is also known that it acts as a phase transfer catalyst like 18-crown-6. The thermodynamic properties of solutions of Bu4NBr yielded much information about structural interactions and lead to development of concept of hydrophobic interactions and cation–cation attractions [16], [17].
The transfer thermodynamic properties have been proved to yield important structural information since they eliminate the standard state required to be fixed for thermodynamic properties of solutions in binary or ternary solutions [18]. The solutions of Ar, Kr have been studied in hydrocarbons as well as in water and the corresponding thermodynamic transfer functions were obtained [19]. The results supported the concept of iceberg formation around solute molecule [20].
In the present work, we report density and sound speed measurements at T = 298.15 K for Bu4NBr in benzene and CCl4 solutions. The data are compared with aqueous solvent system and further used to obtain apparent molar volume and compressibility of Bu4NBr in benzene and CCl4. The results are discussed on the basis of transfer volume and compressibility from non-aqueous to aqueous environment. A possible method of determination of hydration number of organic compressible ions such as Bu4N+ in aqueous solutions is suggested and its usefulness is indicated.
Section snippets
Experimental
Bu4NBr (purity is >99%) procured from MERCK Schurchardt was used after drying in a vacuum oven for several days at room temperature. The benzene and CCl4 used for solutions are of spectroscopy grade from Thomas Baker and used after careful distillation. The concentration of Bu4NBr in benzene and CCl4 were made on molality basis. The water used for density measurement as standard for determination of instrumental constants was freshly prepared doubly quartz distilled deionized water.
The
Results and discussion
The variation of sound speed (u) parameter (Δu = usolution − usolvent) as a function of mole fraction (x2) of Bu4NBr in benzene as well as in CCl4 at T = 298.15 K is shown in figure 1. The sound speed increases with x2 of Bu4NBr in both the solvent systems but the increase is found to be more in CCl4 solutions as compared to solutions in benzene. The data obtained for density values (Δρ = ρsolution − ρsolvent) for Bu4NBr in both solvent systems are depicted in figure 2 as a function of x2 of Bu4NBr at T =
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