Amines

Hardchemistry

The value of pKa of anilinium ion (C6H5NH3+) at 25 C is closest to (Given: Kb of aniline = 4.3 x 10-10):

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$9.37$

$4.63$

$10.57$

$3.43$

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Subject: chemistry
Chapter: organic compounds containing nitrogen
Topic: amines
Difficulty: Hard
Year: 2025

Solution

Correct Answer:

$4.63$

For a conjugate acid-base pair at 25 C, pKa + pKb = 14. First find pKb of aniline: pKb = -log(4.3 x 10-10) approximately 9.37. Therefore pKa of anilinium ion = 14 - 9.37 = 4.63. This low pKa is consistent with weak basicity of aniline, which arises from resonance delocalization of the lone pair on nitrogen into the benzene ring.

This hard difficulty chemistry question is from the chapter organic compounds containing nitrogen, covering the topic of amines. It appeared in the 2025 exam.

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Amines

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