Single Choice

The violet colour obtained during the test of sulphur by Lassaigne's test is due to the formation of:

A$$ Na_2[ Fe(CN)_5S] $$
B$$ Na_2[Fe(CN)_5NO] $$
C$$ Na_2[Fe(CN)_6 ] $$
D$$ Na_4[Fe(CN)_5NOS ] $$
Correct Answer

Solution

During the preparation of Lassaigne's extract, sulphur from the organic compound reacts with sodium to form sodium sulphide. It gives a purple colour with sodium nitroprusside due to the formation of sodium thionitroprusside.

$$2Na+\underset{(From\ organic\ compound)}{S}\rightarrow \ \ Na_{2}S$$

$$\underset{from\ sodium\ exteracted}{Na_{2}S}+Na_{2}[Fe(CN)_{5}NO]\rightarrow \underset{violet colouration}{Na_{4}[Fe(CN)_{5}NOS]}$$

$$\mathbf{Hence\ the\ correct\ answer\ is\ option\ (D).}$$

SIMILAR QUESTIONS

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