Question

Appearance of blood red colour on treatment of the sodium fusion extract of an organic compound with FeSO₄ in presence of concentrated H₂SO₄ indicates the presence of element(s).

• A. N & S
• B. Br
• C. S
• D. N

Answer 1

The Correct Option is A

The presence of specific elements in an organic compound can be identified by observing a blood red color, a phenomenon explained by the underlying chemistry of the test.

1. When an organic compound containing nitrogen and sulfur undergoes sodium fusion, these elements, along with halogens, convert into their respective ionic sodium salts. Specifically, nitrogen in the organic compound reacts with sodium to yield sodium cyanide (NaCN).
2. The subsequent addition of ferrous sulfate (FeSO₄) initiates a reaction, a variant of Lassaigne's test, designed to detect nitrogen by its incorporation into a cyanide complex.
3. The formation of this complex proceeds via the following steps:
   • Sodium cyanide (NaCN) reacts to form a Fe²⁺ cyanide complex.
   • The stoichiometry of this reaction is: \(6NaCN + FeSO\_4 \rightarrow Na\_4[Fe(CN)\_6] + Na\_2SO\_4\)
   • The resulting sodium ferrocyanide, Na₄[Fe(CN)₆], then interacts with ferric ions. These ferric ions are generated in situ through the oxidation of Fe²⁺ by concentrated sulfuric acid, leading to: \(3Na\_4[Fe(CN)\_6] + 4Fe^{3+} + 12H^+ \rightarrow Fe_4[Fe(CN)\_6]_3 + 12Na^+ + 6H_2O\)
   • While the presence of nitrogen alone would produce a Prussian blue color, the simultaneous presence of sulfur results in a blood red color. This distinct coloration is attributed to the formation of ferric thiocyanate (Fe(SCN)₃).
4. Consequently, the characteristic blood red color, indicative of ferric thiocyanate, signifies the co-existence of both nitrogen and sulfur in the original organic compound.

Thus, a blood red color observed during this test confirms the presence of both nitrogen and sulfur in the organic compound.

Correct Answer: N & S