Chemistry · Practical Organic Chemistry

NEET (UG) 2023 — Question 52

In Lassaigne's extract of an organic compound, both nitrogen and sulphur are present, which gives blood red colour with $\mathrm{Fe}^{3+}$ due to the formation of -

Option A:
$NaSCN$
Option B:
$\left[\mathrm{Fe}(\mathrm{CN})_{5} \mathrm{NOS}\right]^{4-}$
Option C:
$[\mathrm{Fe}(\mathrm{SCN})]^{2+}$
Correct
Option D:
$\mathrm{Fe}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]_{3} \cdot \mathrm{xH}_{2} \mathrm{O}$

Answer: C

Step-by-step solution

In case, nitrogen and sulphur both are present in organic compound, sodium thiocyanate is formed.

It gives blood red colour and no Prussian blue since there are no free cyanide ions.

&\mathrm{Na}+\mathrm{C}+\mathrm{N}+\mathrm{S} \longrightarrow \mathrm{NaSCN}\\ &\text { } \end{aligned}$$ $$\begin{aligned} &\mathrm{Fe}^{3+}+\mathrm{SCN}^{-} \longrightarrow[\mathrm{Fe}(\mathrm{SCN})]^{2+}\\ &\text { Blood red } \end{aligned}$$

Answer key and solution verified before publishing.

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Exam: NEET (UG) 2023
Paper: 2023 paper
Subject: Chemistry
Chapter: Practical Organic Chemistry
Topic: Qualitative organic analysis