Activity coefficients and association of n-alkanols in n-octane

Abstract

The infra-red absorption at 1.405 µm, due to O—H stretching, has been determined for solutions of n-dodecanol and of n-octanol up to concentrations of 0.13 mol dm^–3 in n-octane. On the assumptions that the systems behave as ideal associated solutions, and that the absorbance at 1.405 µm is due solely to OH groups in unassociated alcohol, solute activity coefficients have been calculated. The values for dodecanol agree well with those determined previously for the same system, using vapour pressure osmometry, justifying the assignment of the absorption at 1.405 µm to monomeric alcohol alone.

The activity coefficients have been used to estimate the nature and extent of association. It is concluded that for concentrations up to 0.13 mol dm^–3 more than one associated species coexist.