The Partial Molal Volumes of Normal Chain Alcohols in Water–Ethanol Mixtures at 25 °C

The partial molal volumes (0) of n-alcohols (RmOH, m=1–7) at an infinitely dilute concentration in water–ethanol mixtures of various compositions have been determined by means of dilatometry. The 0 value does not depend on the concentration of the solute alcohol within the region studied in any composition of the solvent mixtures. The excess volume, the difference between 0 and the molal volume (V0), is negative and is at a minimum in water-rich mixtures (<16 wt% ethanol) for all of the alcohols studied. On the other hand, in the moderate composition range the excess volumes for R4OH and higher alcohols are positive and reach a maximum distinct from the disappearance of the maximum for R3OH and lower alcohols. The volumetric contribution of a methylene group () to 0 was separately evaluated. From the results, a linear relation was found between 0 and the alkyl chain length of the alcohols in the mixtures of 0–8 and 55–100 wt% ethanol, while in the mixtures the relationship was rather quadratic. Such volumetric behavior was discussed on the basis of the structural properties of the water–ethanol mixtures.