JEE Main 2025 Jan 28 Shift 1, Chemistry Q18: Properties of Carboxylic acids

JEE Main2025Jan 28, Shift 1Chemistry

The compounds that produce CO $_{2}$ with aqueous NaHCO $_{3}$ solution are :

Choose the correct answer from the options given below :

A
A and C only
B
A, B and E only
C
A, C and D only
D
A and B only

Solution

Aqueous NaHCO $_{3}$ liberates CO $_{2}$ only from acids stronger than carbonic acid (pKa $\approx$ 6.35). Carboxylic acids (pKa $\approx$ 4–5) qualify; ordinary phenols (pKa $\approx$ 10) do not. Picric acid is an exception with pKa $\approx$ 0.4 because three electron-withdrawing nitro groups stabilise the phenoxide.

A benzoic acid: carboxylic acid, reacts with NaHCO $_{3}$ . ✓
B phenol: too weak (pKa $\approx$ 10), no reaction. ✗
C 2,4,6-trinitrophenol (picric acid): strong enough, reacts. ✓
D cyclohexanecarboxylic acid: carboxylic acid, reacts. ✓
E p-methoxyphenol: methoxy donates by resonance, making the phenol even weaker; no reaction. ✗

$∴$ A, C and D only.

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JEE Main 2025 Jan 28 Shift 1, Chemistry Q18: Properties of Carboxylic acids

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