Which of the following binary mixture does not show the behavior of minimum boiling azeotropes?
Show Hint
- \( \text{CS}_2 + \text{CH}_3\text{COCH}_3 \)
- \( \text{H}_2\text{O} + \text{CH}_3\text{COC}_2\text{H}_5 \)
- \( \text{C}_6\text{H}_5\text{OH} + \text{C}_6\text{H}_5\text{NH}_2 \)
- \( \text{CH}_3\text{OH} + \text{CHCl}_3 \)
The Correct Option is C
Approach Solution - 1
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.
Approach Solution -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)
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