JEE Main · 2004 · 24 Apr 2004 · Offline · Practical and Analytical Chemistry

The compound formed in the positive test for nitrogen with the Lassaigne solution of an organic compound is

(A) $Fe_{4} [Fe (CN)_{6}]_{3}$ ✓ Correct
(B) $Na_{4} [Fe (CN)_{5} NOS]$
(C) $Fe (CN)_{3}$
(D) $Na_{3} [Fe (CN)_{6}]$

Answer: (A)

Solution

In Lassaigne's test the organic compound is fused with sodium, so any nitrogen ends up as sodium cyanide. Treating the extract with freshly prepared iron(II) sulphate and then acidifying brings up the deep blue precipitate Prussian blue,

Fe X_{4} [Fe (CN) X_{6}] X_{3}

, and it is the forming of this compound that marks the presence of nitrogen.

JEE Main · 2004 · 24 Apr 2004 · Offline · Single correct option

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