Question

Mixtures that can form low boiling azeoptrope among the following are:

• A. Carbon tetrachloride + methanol
• B. Carbon disulphide + acetone
• C. Benzene + toluene
• D. Phenol + aniline

Answer 1

Answer: (A), (B)

Carbon disulphide + acetone

When intermolecular attraction between two components $A$ and $B$ in the mixture is smaller than that between $A$ and $A$ or $B$ and $B$. Then it shows positive deviation from Raoult's law as mixture is more vapourised and boiling point is lowered. They form a low boiling azeotrope at a certain composition. Azeoptropic mixture boils at constant composition.
(a) Methanol molecules possess hydrogen bonding. In a mixture of methanol and carbon tetrachloride, extent of $H-$bonding is decreased. Mixture is more vaporised, thus positive deviation from Raoult's law.
(b) Acetone molecules have higher intermolecular attraction due to dipole-dipole interaction. With $C{S}_2$, this interaction is decreased. Thus, mixture of acetone and $C{S}_2$ shows positive deviaion.
(c) Mixture of benzene and toluene forms ideal solution.
(d) Phenol and aniline possess intermolecular $H-$Bonding. Hence, mixture of phenol and aniline shows negative deviation.