Abstract

Densities of binary mixtures of N,N-dimethylacetamide (DMA) with water (H 2O) or water- d 2 (D 2O) were measured at the temperatures from T=277.13 K to T=318.15 K by means of a vibrating-tube densimeter. The excess molar volumes V m E, calculated from the density data, are negative for the (H 2O + DMA) and (D 2O + DMA) mixtures over the entire range of composition and temperature. The V m E curves exhibit a minimum at x(DMA)≅0.4. At each temperature, this minimum is slightly deeper for the (D 2O + DMA) mixtures than for the corresponding (H 2O + DMA) mixtures. The difference between D 2O and H 2O systems becomes smaller when the temperature increases. The V m E results were correlated using a modified Redlich–Kister expansion. The partial molar volume of DMA plotted against x(DMA) goes through a sharp minimum in the water-rich region around x(DMA)≅0.08. This minimum is more pronounced the lower the temperature and is deeper in D 2O than in H 2O at each temperature. Again, the difference becomes smaller as the temperature increases. The excess expansion factor α E plotted against x(DMA) exhibit a maximum in the water rich region of the mole fraction scale. At each temperature, this maximum is higher for the (D 2O + DMA) mixtures than for the corresponding (H 2O + DMA) mixtures, and the difference becomes smaller as the temperature increases. At its maximum, α E can be even more than 25 per cent of total value of the cubic expansion coefficient α in the (H 2O + DMA) and (D 2O + DMA) mixtures.

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