Which of the following binary mixtures does not show the behaviour of minimum boiling azeotropes?
- CH3OH + CHCl3
- C6H5OH + C6H5NH2
- H2O + CH3COC2H5
- CS2 + CH3COCH3
Answer
(2) C6H5OH + C6H5NH2
Solution
Minimum boiling azeotropes are formed by solutions showing large positive deviation from Raoult's law (A–B attractions weaker than A–A and B–B).
(1) CH3OH + CHCl3: hydrogen bonds among methanol molecules are broken positive deviation.
(3) H2O + CH3COC2H5: hydrogen bonding of water is disturbed positive deviation.
(4) CS2 + CH3COCH3: dipolar interactions of acetone are weakened positive deviation.
(2) C6H5OH + C6H5NH2: a strong intermolecular hydrogen bond C6H5O-H NH2C6H5 forms negative deviation maximum boiling azeotrope.
Phenol + aniline does not form a minimum boiling azeotrope.
Answer: (2)