Appeared in: 2025 (2 sets)
Assertion ($A$) : A mixture of $o$-nitrophenol and $p$-nitrophenol can be separated by steam distillation.
Reason ($R$) : $o$-nitrophenol is steam volatile due to intermolecular hydrogen bonding.
✓ Verified CBSE Marking Scheme
Official Evaluation Steps & EL10 Insight
Question: Assertion (A): A mixture of o-nitrophenol and p-nitrophenol can be separated by steam distillation. Reason (R): o-nitrophenol is steam volatile due to intermolecular hydrogen bonding.
Official CBSE Marking Scheme Solution:
- Step 1 (Conceptual Basis): [0.25 Mark] The separation of o-nitrophenol and p-nitrophenol depends on the nature of hydrogen bonding present in their respective molecules. o-Nitrophenol exhibits intramolecular hydrogen bonding, whereas p-nitrophenol exhibits intermolecular hydrogen bonding.
- Step 2 (Step-by-Step Analysis): [0.50 Mark] Due to intramolecular H-bonding, o-nitrophenol exists as discrete molecules with low molecular association, making it steam volatile. Conversely, p-nitrophenol molecules associate via intermolecular H-bonding, resulting in a higher boiling point and lower volatility. Therefore, the Assertion (A) is True. However, the Reason (R) states that o-nitrophenol is volatile due to intermolecular hydrogen bonding, which is scientifically incorrect. Therefore, the Reason (R) is False.
- Step 3 (Final Concluded Answer): [0.25 Mark] The correct option is: Assertion (A) is true, but Reason (R) is false.
💡 EL10 Concept Insight: Think of o-nitrophenol like a person hugging themselves (intramolecular)—they are compact and can easily "fly away" (evaporate) with steam. p-Nitrophenol is like people holding hands in a long chain (intermolecular)—they are stuck together and much harder to pull apart, so they don't evaporate easily.