Question

Which of the following binary mixture does not show the behavior of minimum boiling azeotropes?

• A. \( \text{CS}_2 + \text{CH}_3\text{COCH}_3 \)
• B. \( \text{H}_2\text{O} + \text{CH}_3\text{COC}_2\text{H}_5 \)
• C. \( \text{C}_6\text{H}_5\text{OH} + \text{C}_6\text{H}_5\text{NH}_2 \)
• D. \( \text{CH}_3\text{OH} + \text{CHCl}_3 \)

Hint:

- Minimum boiling azeotropes: Positive deviation (weaker interactions) - Maximum boiling azeotropes: Negative deviation (stronger interactions) - Look for H-bonding capability differences between components - Similar molecules (like phenol + aniline) tend to form maximum boiling azeotropes

Answer 1

The Correct Option is C

This question asks which binary mixture does not form a minimum boiling azeotrope. An azeotrope is a mixture of two or more liquids whose proportions cannot be altered by simple distillation. They have a constant boiling point. Minimum boiling azeotropes have a boiling point lower than either of their individual components.

Let's evaluate each option:

• \(\text{CS}_2 + \text{CH}_3\text{COCH}_3\): Carbon disulfide and acetone form a minimum boiling azeotrope because of the strong interactions differing from ideal solutions, which lowers the boiling point.
• \(\text{H}_2\text{O} + \text{CH}_3\text{COC}_2\text{H}_5\): Water and ethyl acetate also form a minimum boiling azeotrope. Despite water's strong hydrogen bonding, the solvent interactions disrupt this, leading to an azeotrope.
• \(\text{C}_6\text{H}_5\text{OH} + \text{C}_6\text{H}_5\text{NH}_2\): Phenol and aniline do not form an azeotrope. They have significant specific interactions like hydrogen bonding, not favoring azeotopic behavior.
• \(\text{CH}_3\text{OH} + \text{CHCl}_3\): Methanol and chloroform form a minimum boiling azeotrope due to their interaction which lowers the boiling point.

Therefore, the correct answer is \(\text{C}_6\text{H}_5\text{OH} + \text{C}_6\text{H}_5\text{NH}_2\) as they do not form such an azeotrope due to the specific interactions between the two components that stabilize their separate phases more than their mixture.

Answer 2

Key Concept: 
Minimum boiling azeotropes form when:
- Components show positive deviation from Raoult's law
- Molecular interactions between unlike molecules are weaker than between like molecules
- Typically occurs between molecules with different polarity or hydrogen bonding capacity

Analysis of Options:
- Option 1: CS₂ + CH₃COCH₃
- Carbon disulfide (non-polar) + acetone (polar)
- Forms minimum boiling azeotrope (shows positive deviation)
- Option 2: H₂O + CH₃COC₂H₅
- Water (strong H-bonding) + methyl ethyl ketone (weak H-bonding)
- Forms minimum boiling azeotrope
- Option 3: C₆H₅OH + C₆H₅NH₂
- Phenol + aniline (both can form strong intermolecular H-bonds)
- Shows negative deviation (forms maximum boiling azeotrope)
- Correct answer as it doesn't form minimum boiling azeotrope
- Option 4: CH₃OH + CHCl₃
- Methanol + chloroform (forms H-bonded complex)
- Shows positive deviation (minimum boiling azeotrope)