Three students, Manish, Ramesh and


Three students, Manish, Ramesh and Rajni were determining the extra

elements present in an organic compound given by their teacher. They

prepared the Lassaigne’s extract (L.E.) independently by the fusion of the

compound with sodium metal. Then they added solid FeSO4 and dilute

sulphuric acid to a part of Lassaigne’s extract. Manish and Rajni obtained

Prussian blue colour but Ramesh got a red colour. Ramesh repeated the test

with the same Lassaigne’s extract but again got red colour only. They were

surprised and went to their teacher and told him about their observation.

A teacher asked them to think over the reason for this. Can you help them by

giving the reason for this observation? Also, write the chemical equations to

explain the formation of compounds of different colours


3NaCNS + FeSO4 + dilute sulphuric→ Fe(CNS)3 (Blood red colour) + 3Na+

Ramesh has Nitrogen as well as Sulphur present in his organic compound so, he was observed the Blood-red colour of Fe(CNS)3 and Manish and Rajni were having only Nitrogen in their compound, hence they got Prussian blue colour.

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