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

Abstract

Densities of binary mixtures of N, N -dimethylformamide (DMF) with water (H2 O) or water- d2(D 2O) were measured at the temperatures from 277.13 K to 318.15 K by means of a vibrating-tube densimeter. The excess molar volumes VmE, calculated from the density data, are negative for the (H 2O + DMF) and (D 2O + DMF) systems over the entire range of composition and temperature. TheVmE curves exhibit a minimum at x (H 2O or D 2O) ∼= 0.6. At each temperature this minimum is slightly deeper for the (D 2O + DMF) than for the corresponding (H 2O + DMF). The difference between D2 O and H 2O systems becomes smaller when the temperature increases. TheVmE results were correlated using a modified Redlich–Kister expansion. The partial molar volume of DMF plotted against x (H 2O or D 2O) goes through a sharp minimum in the water-rich region around x (H 2O or D 2O) ∼= 0.92. 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 αE plotted against x (H 2O or D 2O) exhibit a maximum in the water rich region of the mole fraction scale. At each temperature, this maximum is higher for the (D 2O + DMF) than for the corresponding (H2 O + DMF). At T= 277.134 K, the maximum is located at x (H2 O or D 2O) ∼= 0.8 and is shifting slightly towards lower x (H2 O or D 2O) with increasing temperature. At its maximum, αE can be even more than 25 per cent of total value of the cubic expansion coefficient α in the (H 2O + DMF) and (D 2O + DMF). The experimental data ofVmE and the literature data ofHmE were used to test the applicability of the extended real association solution (ERAS) model for describing the both excess properties. For all the mixtures theVmE and HmE 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.