J Solution Chem (2009) 38: 441–448 DOI 10.1007/s10953-009-9383-6 Acoustic and Thermodynamic Properties of Binary Liquid Mixtures of Benzaldehyde in Hexane and Cyclohexane S. Azhagiri · S. Jayakumar · R. Padmanaban · S. Gunasekaran · S. Srinivasan Received: 10 September 2008 / Accepted: 14 December 2008 / Published online: 13 February 2009 © Springer Science+Business Media, LLC 2009 Abstract Densities and ultrasonic speeds of binary mixtures of benzaldehyde with n- hexane and cyclohexane at 30 °C were measured over the entire composition range. From these experimental data, the adiabatic compressibility (K S ), intermolecular free length (L f ), acoustic impedance (Z), relative association (R a ) and relaxation strength (r) were cal- culated. Also, the excess adiabatic compressibility (K E S ), intermolecular free length (L E f ), acoustic impedance (Z E ), and ultrasonic velocity (U E ) were calculated. The observed varia- tion of these parameters helps in understanding the nature of interactions in these mixtures. Further, theoretical values of the ultrasonic speed were evaluated using theories and empiri- cal relations. The relative merits of these theories and relations were discussed. Keywords Ultrasonic velocity · Benzaldehyde · Hexane · Cyclohexane 1 Introduction Ultrasonic measurements are extensively used to study molecular interactions in pure liquids and liquid mixtures. The study of the solution properties of liquid mixtures finds applications S. Azhagiri PG and Research Department of Physics, Pachaiyappa’s College, Chennai, India S. Jayakumar PG and Research Department of Physics, RKM Vivekananda College, Chennai, India R. Padmanaban Department of Physics, Sri Chandrasekharendra Saraswathi Viswa Maha Vidyalaya University, Enathur, Kancheepuram, India S. Gunasekaran Registrar, Periyar University, Salem, India S. Srinivasan ( ) Department of Physics, L. N. Government College, Ponneri, India e-mail: dr_s_srinivasan@yahoo.com