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.