Question:
When sodium fusion extract is treated with sodium nitroprusside, the appearance of violet colour is due to the formation of
When sodium fusion extract is treated with sodium nitroprusside, the appearance of violet colour is due to the formation of
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Lassaigne’s test:
- Sulphur $\rightarrow$ violet colour with sodium nitroprusside
Updated On: Apr 30, 2026
- $[\mathrm{Fe(CN)_5NO}]^{2-}$
- $[\mathrm{Fe(CN)_5NO}]^{2+}$
- $[\mathrm{Fe(CN)_5NOS}]^{4-}$
- $[\mathrm{Fe(CN)_5NOS}]^{2-}$
- $[\mathrm{Fe(CN)_5NOS}]^{2+}$
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The Correct Option is C
Solution and Explanation
Concept:
Sodium fusion test (Lassaigne’s test) for sulphur:
• Sulphur forms $\mathrm{Na_2S}$ in sodium extract
• On treatment with sodium nitroprusside, a violet complex is formed
Step 1: Reaction involved.
\[ \mathrm{Na_2S + [Fe(CN)_5NO]^{2-} \rightarrow [Fe(CN)_5NOS]^{4-}} \]
Step 2: Observation.
Formation of violet coloured complex confirms sulphur.
Step 3: Conclusion.
The complex formed is: \[ [\mathrm{Fe(CN)_5NOS}]^{4-} \]
• Sulphur forms $\mathrm{Na_2S}$ in sodium extract
• On treatment with sodium nitroprusside, a violet complex is formed
Step 1: Reaction involved.
\[ \mathrm{Na_2S + [Fe(CN)_5NO]^{2-} \rightarrow [Fe(CN)_5NOS]^{4-}} \]
Step 2: Observation.
Formation of violet coloured complex confirms sulphur.
Step 3: Conclusion.
The complex formed is: \[ [\mathrm{Fe(CN)_5NOS}]^{4-} \]
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