Volumetric properties of binary mixtures of N,N-dimethylformamide with water or water-d2 at temperatures from 277.13 K to 318.15 K

Densities of binary mixtures of N,N-dimethylformamide (DMF) with water (H2O) or water-d(2) (D2O) were measured at the temperatures from 277.13 K to 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 (H2O + DMF) and (D2O + DMF) systems over the entire range of composition and temperature. The V-m(E) curves exhibit a minimum at x(H2O or D2O) congruent to 0.6. At each temperature this minimum is slightly deeper for the (D2O + DMF) than for the corresponding (H2O + DMF). The difference between D2O and H2O 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 DMF plotted against x(H2O or D2O) goes through a sharp minimum in the water-rich region around x(H2O or D2O) congruent to 0.92. This minimum is more pronounced the lower the temperature and is deeper in D2O than in H2O at each temperature. Again, the difference becomes smaller as the temperature increases. The excess expansion factor alpha(E) plotted against x(H2O or D2O) exhibit a maximum in the water rich region of the mole fraction scale. At each temperature, this maximum is higher for the (D2O + DMF) than for the corresponding (H2O + DMF). At T = 277.134 K, the maximum is located at x(H2O or D2O) congruent to 0.6 and is shifting slightly towards lower x(H2O or D2O) with increasing temperature. At its maximum, alpha(E) can be even more than 25 per cent of total value of the cubic expansion coefficient alpha in the (H2O + DMF) and (D2O + DMF). The experimental data of V-m(E) and the literature data of H-m(E) were used to test the applicability of the extended real association solution (ERAS) model for describing the both excess properties. For all the mixtures the V-m(E) and H-m(E) values, calculated by ERAS, are of the same sign as the experimental values. Small deviations in the symmetry of the predicted curves are, however, observed. (C) 2002 Elsevier Science Ltd. All rights reserved.