The ultrasonic velocity (u) and density (rho) of binary mixtures of formamide (FA) with 2-methoxyethanol (2-ME) and 2-ethoxyethanol (2-EE) have been measured over the entire composition range at temperatures (303.15, 313.15, and 323.15) K. The experimental values of ultrasonic velocities and densities have been used to determine the adiabatic compressibility (beta(S)), intermolecular free length (L-f), molar sound velocity (R), molar compressibility (B), and specific acoustic impedance (Z). The excess values of ultrasonic velocity (u(E)), adiabatic compressibility (beta(E)(S)), acoustic impedance (Z(E)), and molar volume (V-m(E)) were also calculated. The observed variations of these parameters, with composition and temperature, are discussed in terms of the molecular interactions due to physical, chemical, and structural effects between the unlike molecules of the binary mixtures. Further, the infrared spectra of both the systems, (FA + 2-ME) and (FA + 2-EE), have also been recorded at room temperature and found to be useful for understanding the presence of extensive hydrogen bonding between oxygen atom of C=O group of formamide and hydrogen atoms of the H-O group of 2-alkoxyethanol molecules in these binary liquid mixtures. (C) 2012 Elsevier Ltd. All rights reserved.