Thermodynamic properties of aqueous organic solutes in relation to their structure. Part III. Apparent molal volumes and heat capacities of low molecular weight alcohols and polyols at 25 °C

The density and specific heat of dilute aqueous solutions of various alcohols and polyols have been measured at 25 °C. Such measurements have been carried out for the following solutes: methanol, ethanol, n-propanol, n-butanol, isobutanol, s-butanol, tert-butyl alcohol, n-pentanol. 3-pentanol, neo-pentanol, ethyleneglycol, 1,4-butanediol, 1,6-hexanediol, dimethyl-2,2-propanediol, 1,1,1-tris(hydroxymethyl)ethane, and pentaerythritol.The limiting apparent molal volume Formula: see text and heat capacities Formula: see text derived from these data exhibit some variations among the properties of isomers (e.g. branched vs. normal alkyl groups), but these variations cannot be conclusively attributed to specific effects in the hydration of the alkyl groups. On the other hand, the data allows one to derive group contributions to Formula: see text and Formula: see text namely Formula: see text for the methylene group, Formula: see text for the OH functional group and Formula: see text for the C—H of a terminal methyl group.The concentration dependence of Formula: see text brings out some interesting new features. With most of the alcohols, Formula: see text decreases with concentration, in a way related to the degree of hydrophobicity of the alcohol. Solute–solute interactions contribute to reduce Formula: see text of the hydrophilic solutes, but the opposite effect is observed with the most hydrophobic alcohols.