CBSE Class 12 · 2005 · All India Compartment · Compounds Containing NitrogenShort Answer

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Give reasons:
a) Methylamine in water reacts with ferric chloride to precipitate ferric hydroxide.
b) Aromatic amines are less basic than aliphatic amines.

Answer: (a) CH₃NH₂ makes the solution basic (OH⁻), which precipitates Fe(OH)₃. (b) The aryl ring delocalises the N lone pair.

Solution

(a) Methylamine generates hydroxide:

C H_{3} N H_{2} + H_{2} O ⇌ C H_{3} N H_{3}^{+} + O H^{-}; F e^{3 +} + 3O H^{-} \to Fe (OH)_{3} ↓ (brown)

(b) In arylamines the lone pair conjugates into the ring and the arylammonium ion loses that resonance — protonation is disfavoured relative to alkylamines.

CBSE Class 12 Board · 2005 · All India Compartment · Subjective

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