Density, speed of sound, and refractive index measurements for the binary systems (butanoic acid + propanoic acid, or 2-methyl-propanoic acid) at T = (293.15 to 313.15) K

Density, speed of sound, and refractive index for the binary systems (butanoic acid + propanoic acid, or 2-methyl-propanoic acid) were measured over the whole composition range and at T = (293.15, 298.15, 303.15, 308.15, and 313.15) K. The excess molar volumes, isentropic compressibilities, excess isentropic compressibilities, molar refractions, and deviation in refractive indices were also calculated by using the experimental densities, speed of sound, and refractive indices data, respectively. The Redlich–Kister smoothing polynomial equation was used to fit the excess molar volume, excess isentropic compressibility and deviation in refractive index data. The thermodynamic properties have been discussed in terms of intermolecular interactions between the components of the mixtures.

►  VmE for (butyric acid + propanoic acid) is positive and negative for (butyric acid + isobutyric acid). ►  κsE is positive for (butanoic acid + propanoic acid). ►  κsE is both positive and negative for (butanoic acid + 2-methyl-propanoic acid). ► Δn values are negative for the system (butyric acid + propanoic acid). ► Δn values are positive for the system (butyric acid + isobutyric acid) at all temperatures.