Excess molar volumes of carboxylic acid mixtures: binary mixtures of formic, acetic, propionic, n-pentanoic and iso-pentanoic acids at 298.15 K

Systematic measurements of density were performed in six binary mixtures of carboxylic acids. Derived from the densities the excess molar volumes V^E are always positive, with the exception of the formic acid+acetic acid system where V^E is negative for x<0.75 and positive for mixtures rich in formic acid. The extremal values of V^E are about -0.06 and +0.02 cm² mol^-1. As a rule, the excess molar volume curves are slightly asymmetrical with respect to composition having the maximal values of about 0.15 cm³ mol^-1 in the formic acid+propionic acid system; 0.10 cm³ mol^-1 in the acetic acid+ propionic acid system; 0.35 cm³ mol^-1 in the acetic acid+n-pentanoic acid system; 0.65 and 0.62 cm³ mol^-1 in the systems of n-pentanoic and iso-pentanoic acids with formic acid. A qualitative interpretation of the presented results is given taking into account almost complete dimerization of carboxylic acids and the formation of mixed dimers of these acids.