Refractive index and excess volume for binary liquid mixtures. Part 1.—Analyses of new and old data for binary mixtures

Abstract

The relation between the refractive index and the excess molar volume for binary liquid mixtures has been clarified using the additivity rule. The excess volume is represented by two terms due to the excess refractive index and the refractive index difference. Refractive indices have been measured by a differential refractometer for the isorefractive binary mixtures 1-chlorobutane (BuCl)–butan-2-ol (BuOH), 1-chlorobutane–2-methoxyethanol (MOEt), and isopropyl acetate (IPA)–methylethyl ketone (MEK). For the isorefractive binary systems the excess volume was represented by the excess refractive index term and compared with the observed one without knowing the explicit form of the refractive index equation. Coherent correlations were found between the observed excess volume and refractive index for the systems BuCl–BuOH and BuCl–MOEt. The relation of the excess volume and refractive index for the system IPA–MEK suggested a contradiction to the additivity rule. The analyses of the old data for the system propan-1-ol–1,2-dibromoethane have elucidated a strong dependence of the refractive index difference term on the functional form of the refractive index equation. The binary systems studied are not described by a unique equation for the refractive index.