Ultrasonic velocity, viscosity and density of alcohol [s] in n-hexane have been measured at various temperatures in the range of 303.15 -318.15K. From the experimental data, the acoustical parameters such as molar volume, adiabatic compressibility, intermolecular free length and their excess values have been computed and presented as functions of compositions. The deviations from ideality of the acoustical parameters are explained on the basis of molecular interactions between the components of the mixtures. The variations of these parameters with composition of the mixture suggest the strength of interactions in these mixtures.

Ultrasonic velocities and densities of the binary liquid mixtures of benzene with 1-propanol, 2-propanol, 1-butanol, 2-butanol and 3-butanol at 303.15 to 318.15 K, over the entire composition range were measured. The theoretical values of ultrasonic velocity were evaluated using the Nomoto's Relation (NR), Ideal Mixture Relation (IMR), Free Length Theory (FLT) and Collision Factor Theory (CFT). The validity of these relations and theories were tested by comparing the computed sound velocities with experimental values. Further, the molecular interaction parameter (α) was computed by using the experimental and the theoretical ultrasonic velocity values. The variation of this parameter with composition of the mixtures has been discussed in terms of molecular interaction in these mixtures.

The wide spread use of 1,3,4-oxadiazoles as a scaffold in medicinal chemistry establishes this moiety as an important bioactive class of heterocycles. In the present study ultrasonic velocity (u), density (ρ) and viscosity (η) have been measured at frequency 2 MHz in the binary mixtures of 1,3,4-oxadiazole derivatives in acetone at 303.15 K using ultrasonic interferometer technique. The measured value of ultrasonic velocity, density and viscosity have been used to estimate the acoustical parameters namely adiabatic compressibility (β ad ), relaxation time (τ), acoustic impedance (Z i ), free length (L f ), free volume (V f ) and internal pressure (π i ), with a view to investigate the nature and strength of molecular interactions. The obtained result support the occurrence of molecular association through hydrogen bonding in the binary liquid mixtures.

By combining the van der Waals' equation of state and the Free Length Theory of Jacobson, a new theoretical model is developed for the prediction of internal pressure of pure liquids and liquid mixtures. It requires only the molar volume data in addition to the ratio of heat capacities and critical temperature. The proposed model is simple, reliably accurate and capable of predicting internal pressure of pure liquids with an average absolute deviation of 4.24% in the predicted internal pressure values compared to those given in literature. The average absolute deviation in the predicted internal pressure values through the proposed model for the five binary liquid mixtures tested varies from 0.29% to 1.9% when compared to those of literature values. Keywords:van der Waals; pressure of liquids; theory of Jacobson; capacity of heat liquids; equation of Srivastava and Berkowitz INTRODUTIONThe importance of internal pressure in understanding the properties of liquids and the full potential of internal pressure as a structural probe did become apparent with the pioneering work of Hildebrand 1, 2 and the first review of the subject by Richards 3 appeared in 1925. In an excellent article Dack 4 reviewed the importance of solvent internal pressure and cohesion to solution phenomena. A review on the relationship between the intermolecular forces and properties of solution was made by Kortum 5 . Barton 6 discussed the relationship between internal pressure and molar volume in some depth. Pointing out that internal pressure is a uniquely important parameter in sonochemistry, Srivastava and Berkowitz 7 developed an expression, which permits the evaluation of internal pressure from readily available and easily measurable quantities. In this work a simple equation is proposed by incorporating the Free Length Theory of Jacobson 8,9 and van der Waals' equation of state; the proposed model is a purely predictive tool for predicting internal pressure of liquids and liquid mixtures. Computed internal pressure values for liquids and liquid mixtures through the proposed equation are compared with those of literature.

No abstract