1 Korean J. Chem. Eng., 34(7), 1-13 (2017) DOI: 10.1007/s11814-017-0352-2 INVITED REVIEW PAPER pISSN: 0256-1115 eISSN: 1975-7220 INVITED REVIEW PAPER † To whom correspondence should be addressed. E-mail: Adel.Toumi@fst.rnu.tn Copyright by The Korean Institute of Chemical Engineers. Ultrasonic velocity measurements in isobutyric acid - water binary mixtures over the temperature range from 300.15 to 313.15 K Radhia Trabelsi * , Moncef Bouanz * , ** , and Adel Toumi * ,† *Laboratoire de Physique des Liquides Critiques, Département de Physique, Faculté des Sciences de Bizerte, Zarzouna 7021 Bizerte, Université de Carthage, Tunisia **Unité de Recherche de Physique des Liquides et d’Optique Non Linéaire, Département de Physique, Faculté des Sciences de Tunis, Campus Universitaire, El Manar 2092 Tunis, Université de Tunis El Manar, Tunisia (Received 5 August 2017 • accepted 26 December 2017) AbstractWe measured the ultrasonic velocity, U, density,  , and viscosity,  in Isobutyric acid - water binary liquid mixtures over the entire composition range at temperatures ranging from 300.15 to 313.15 K under atmospheric pres- sure. The experimental data values were analyzed to determine, various acoustical parameters: adiabatic compressibil- ity, , acoustic impedance, Z, free length, L f , free volume, V f , molar volume, V m , relaxation time, , absorption coefficient, /f 2 , internal pressure,  i , Gibb’s free energy, G, cohesive energy, CE, Wada’s constant, W, Rao’s constant, R m and relative association, R A . The variation of these parameters versus the mixture composition was explained on the basis of the intermolecular interactions between the components of the mixture. Keywords: Binary Mixtures, Isobutyric Acid, Water, Molecular Interactions, Ultrasonic Velocity, Acoustical Parameters INTRODUCTION The isobutyric acid - water (IBA-W) system is convenient for studying nonequilibrium interfacial phenomena. The mutual mis- cibility of coexisting liquid phases of this binary liquid is very pro- pitious for innovative separation and extraction processes [1,2]. Moreover, the advantage of studying (IBA-W) mixture which is stable is that it is characterized by a coexistence curve represent- ing a readily accessible way of studying the mixing of molecules. Previously, we studied and reported data for this critical mixture: transport phenomena and physical properties [3,4], ionic struc- ture [5], salvation phenomenon in a binary liquid [6], the effect of ions on the mixture (IBA+W) [7] and phase equilibrium proper- ties occurring in the presence of added ions [8]. In chemical and industrial processes, materials are normally handled in fluid form and consequently, the physical, chemical and transport properties of fluids, are important. Therefore, data on some of the properties associated with the liquids and liquid mix- tures such as ultrasonic velocity, density and viscosity find exten- sive application in solution theory and molecular dynamics. The practical need for thermodynamic data for research, design and set up of industrial processes remains to drive investigation in the study of multicomponent systems. Ultrasonic velocity measurements have been employed to investigate the nature of molecular interac- tions occurring in pure liquids, binary and ternary liquid mixtures [9-13]. It is therefore required to have a data source which gives the speed of sound and the density in the mixtures by simply specify- ing their concentration and temperature. Since the speed of sound has often been measured in-house, a literature survey shows that ultrasonic studies have been made in a large number of binary liq- uid mixtures [14-20]; nevertheless, there are few numerically acces- sible data available for the (IBA-W) system [21-23]. Both Dunker et al. [21] and Belkoura et al. [22] have reported measurements of sound attenuation in the homogeneous phase near the critical mix- ing point of (IBA-W) mixture. The experimental results have been analyzed in terms of a theory of critical ultrasonic absorption pro- posed by Bhattacharjee and Ferrell, which contains no adjustable parameters [24]. Kaatze and Schreiber [23] studied the depen- dence upon frequency of the ultrasonic absorption coefficient for the (IBA-W) system of critical composition as a function of tem- perature; however, the data were presented in graphs instead of numerical values. The spirit of the present work was to perform a detailed experi- mental study of the temperature and concentration dependence of ultrasonic velocity in Isobutyric acid - water (IBA-W) binary mixture. The ultrasonic velocity data were determined in the single phase as a function of six temperatures: 300.15 K, 302.15 K, 305.15 K, 308.15 K, 311.15 K and 313.15 K and of the whole composition x 1 in acid (IBA). These obtained values can be coupled with other experimental data such as density and shear viscosity to compute various acoustical parameters such as adiabatic compressibility,  , acoustic impedance, Z, free length, L f , free volume, V f , molar vol- ume, V m , relaxation time, , internal pressure,  i , absorption coeffi- cient, /f 2 , relative association, R A , Rao’s constant, R m , Wada’s constant, W, Gibbs free energy, G, and cohesive energy, EC. EXPERIMENTAL SECTION 1. Materials Water (CAS No 7732-18-5) was obtained from Merck while