| Abstrakt: |
Apparent molal volumes (φv) at 25 °C have been obtained for the following urea derivatives in water–methanol mixtures from measurements of the density using an Anton Paar digital densimeter: urea (U), methylurea (MU), ethylurea (EU), 1,1-dimethylurea (1,1-DMU), 1,3-dimethylurea (1,3-DMU), 1,1-diethylurea (1,1-DEU), and 1,3-diethylurea (1,3-DEU). The limiting values φv°were calculated by linear extrapolation using the least-squares method. A plot of φv°vs. X2, the mole fraction of methanol, showed a minimum for each alkylurea studied at low methanol concentrations (X2\simeq0.1), but none for unsubstituted urea: the more alkyl-substituted the urea was, the sharper the minimum. Inspection of the data shows that the assumption of independent solvation on both sides of the urea molecules also holds to a good approximation to the apparent molal volumes both in the pure solvents and in the mixtures. |
