Question

In a Lassaigine's test for sulphur in the organic compound with sodium nitroprusside solution the purple colour formed is due to:

• A. $N{a}_4\left[Fe\right(CN{)}_{5}NOS]$
• B. $N{a}_3\left[Fe\right(Cn{)}_{5}S]$
• C. $N{a}_2\left[Fe\right(CN{)}_{5}NOS]$
• D. $N{a}_3\left[Fe\right(CN{)}_6]$

Answer 1

Answer: (A)

$N{a}_4\left[Fe\right(CN{)}_{5}NOS]$

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.