JEE Main 2022 · 29 June · morning · Single correct · +4 / −1
Given below are two statements :
Statement I : Phenols are weakly acidic.
Statement II : Therefore they are freely soluble in NaOH solution and are weaker acids than alcohols and water.
Choose the most appropriate option :
- (a) Both Statement I and Statement II are correct.
- (b) Both Statement I and Statement II are incorrect.
- (c) Statement I is correct but Statement II is incorrect.
- (d) Statement I is incorrect but Statement II is correct.
Answer and solution
Answer (c) Statement I is correct but Statement II is incorrect.
Solution
Chemistry ma’am · 4 steps
Phenol is weak, yes, but it beats water and alcohols. That last clause is what breaks Statement II.
- Statement I. Phenol has pKₐ ≈ 10, so it gives up H⁺ only slightly. It is weakly acidic, and Statement I is correct.
- Why phenol beats alcohols. The phenoxide ion's negative charge spreads into the benzene ring by resonance, which stabilises it. An alkoxide ion like C₂H₅O⁻ has no such resonance, so alcohols lose H⁺ much less readily.
Compound Approximate pKₐ Acid strength Phenol, C₆H₅OH 10 strongest of the three Water, H₂O 15.7 weaker than phenol Ethanol, C₂H₅OH about 16 weaker than phenol - Statement II. Phenols do dissolve in NaOH, because they form water-soluble sodium phenoxide. But a smaller pKₐ means a stronger acid, so phenols are stronger acids than alcohols and water, not weaker. Statement II is incorrect.
- So. Statement I is correct and Statement II is incorrect, which is option (c).
The idea to keep. Acidity order to remember: phenol > water > alcohol. Resonance stabilisation of phenoxide is the reason. Read every clause of a statement, because one wrong comparison makes the whole statement wrong.
Answer from the NTA final answer key. Solution by PrepWiser.