Ultrasonic Investigation of Molecular Interactions in Binary Mixtures at 303 K

The ultrasonic velocity, density and viscosity at 303 K have been measured in the binary systems of toluene with benzene and o-xylone with benzene. The acoustical parameters such as adiabatic compressibility, free length, free volume and acoustical impedance are calculated. The results are interpreted in terms of molecular interaction between the components of the mixtures.


Introduction
In recent years ultrasonic investigation find extensive applications in probing in to the physicochemical behaviour of binary liquid mixtures leading to an understanding of the liquid state [1][2][3] .Ultrasonic technique has been adequately employed to investigate the properties of any substance to understand the nature of molecular interactions in pure liquid 1 liquid mixtures [2][3][4][5] and ionic interactions in electrolytic solutions 6,7 .Though the molecular interactions studies can be best carried out through spectroscopic methods 8,9 the other non spectroscopic techniques such as dielectric 10 magnetic 11 ultrasonic velocity and viscosity 12 measurements have been widely used in field of interactions and structural aspect evaluations studies.The measurements of ultrasonic velocity have been adequately employed in understanding the nature of molecular systems and physicochemical behaviour in liquid mixtures [13][14][15][16] .

Experimental
The Ultrasonic Velocity was measured using a single crystal variable path interferometer working at 2MHz by standard procedure.The accuracy of ultrasonic velocity determination in the solution is ±0.001%.The velocities were measured at room temperature 303 K.The density were measured using a corning specific gravity bottle by standard procedure and the viscosity was measured using Oswald's viscometer with an accuracy of ± .1%.

Results and Discussion
The calculated parameters such as adiabatic compressibility (β), inter molecular free length (L f ), free volume (V f ) and acoustic impedance (Z), are calculated using the following relation (1-4).
(2) 3/2 (3) and The measured values such as ultrasonic velocity (U), density (ρ ) and viscosity (η ) are of o-xylone with benzene and toluene with benzene are given in Table 1.It is clearly reveals that all measured parameters, sound velocity, density and viscosity, increasing and decreasing trend for increasing moles of x 2 .The ultrasonic velocity studies carried out in the present investigation reveal that the velocity varies with concentration due to the solutesolvent interactions through molecular association.The existing particle-particle resistance initiates some more interactions and this is supported by the measured parameters.
A keen look at the Table 1 suggest that the range of density, sound velocity, and their variation with concentration of toluene is appreciable, this liquid composition suggests the basis of structural changes as well as interaction between like molecules and unlike molecules.On comparing toluene and o-xylone, in general, toluene shows a relatively higher density and viscosity.The shear viscosity increases with increase of concentration once again confirmed that the solute -solvent interaction.
Table 1.Measured (Ultrasonic velocity (U), density (ρ) and viscosity (η) and calculated (adiabatic compressibility (β), free length (L f ), free volume (V f ) and acoustical impedance (Z) parameters for benzene + toluene, o-xylone at 303 K. On comparing toluene and o-xylone, the zigzag values are obtained for β, but for o-xylone the increasing trend is observed, its shows that the interaction is higher in the second system.The intermolecular free lengths L f has been calculated by using semi empirical relation given by Jacobson 17 .The values of L f reflects the same trend as that of β.According to Eyring and Kincaid 18 , the ultrasonic velocity increases, if the L f decreases and vice -a -versa in a result of mixing components.The decrease or increase in the values of L f can be explained on the basis of interactions between the solute and solvent molecules.
The values of V f is decrease in trend of both these system suggest that there is a specific interaction between the components of the mixtures.The specific acoustic impedance Z is varied linearly with concentration of solution.