The Partial Molal Volumes of Normal Chain Alcohols in Water–Ethanol Mixtures at 25 °C
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概要
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The partial molal volumes (\bar<I>V</I><SUP>0</SUP>) of <I>n</I>-alcohols (R<I><SUB>m</SUB></I>OH, <I>m</I>=1–7) at an infinitely dilute concentration in water–ethanol mixtures of various compositions have been determined by means of dilatometry. The \bar<I>V</I><SUP>0</SUP> 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 \bar<I>V</I><SUP>0</SUP> and the molal volume (<I>V</I><SUP>0</SUP>), 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 R<SUB>4</SUB>OH and higher alcohols are positive and reach a maximum distinct from the disappearance of the maximum for R<SUB>3</SUB>OH and lower alcohols. The volumetric contribution of a methylene group (\bar<I>V</I><SUP>me</SUP>) to \bar<I>V</I><SUP>0</SUP> was separately evaluated. From the results, a linear relation was found between \bar<I>V</I><SUP>0</SUP> 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.
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