Phenols are acidic in nature. Which of the following statements is incorrect about them?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Phenol liberates carbon dioxide on reaction with sodium bicarbonate.
Phenol is acidic because the phenoxide ion formed on losing \( \ce{H+} \) is stabilised by resonance. It is, however, a weak acid (pKa = 10.0), weaker than carbonic acid. An acid can liberate \( \ce{CO2} \) from sodium hydrogencarbonate only if it is stronger than carbonic acid; carboxylic acids (pKa about 4–5) can, phenol cannot:
\( \displaystyle \ce{RCOOH + NaHCO3 -> RCOONa + H2O + CO2 ^} \)
\( \displaystyle \ce{C6H5OH + NaHCO3} \rightarrow \text{no reaction} \)
Option (1) Phenols are soluble in aqueous alkali solution — Correct about phenols. Phenol reacts with NaOH, forming water-soluble sodium phenoxide: \( \ce{C6H5OH + NaOH -> C6H5ONa + H2O} \).
Option (2) Phenol liberates hydrogen gas on reaction with sodium metal. — Correct about phenols. Like alcohols, phenol reacts with active metals: \( \ce{2C6H5OH + 2Na -> 2C6H5ONa + H2 ^} \).
Option (3) Phenol liberates carbon dioxide on reaction with sodium bicarbonate. — Incorrect about phenols. Phenol is weaker than carbonic acid, so it does not react with sodium hydrogencarbonate; this is the test that tells a carboxylic acid from a phenol.
Option (4) Phenol is less stabilized by resonance than phenoxide ion. — Correct about phenols. The resonance structures of phenol involve separation of charge, while in the phenoxide ion only the negative charge is spread over the oxygen and the ring, so the phenoxide ion is more stable.
NCERT (2026-27 edition):
Reactions with Metals and Alkalies
Acidity of Phenols – “The reactions of phenol with metals (e.g., sodium, aluminium) and sodium hydroxide indicate its acidic nature. … Although there is also charge delocalisation in phenol, its resonance structures have charge separation due to which the phenol molecule is less stable than phenoxide ion.”