NEET2026ChemistryChapterActual
During the qualitative analysis of an organic compound containing both nitrogen and sulphur, fusion is carried out with an excess of sodium metal. When the resulting Lassaigne's extract is treated with Fe³⁺ ions, the characteristic blood-red coloration is not observed. Which of the following best explains this phenomenon?
Options
- AExcess sodium metal reduces Fe³⁺ to Fe²⁺ , preventing the formation of the complex.
- BA colorless sodium hexathiocyanatoferrate(III) complex is formed due to the high concentration of sodium.
- CThe initially formed sodium thiocyanate decomposes to yield sodium cyanide and sodium sulphide.
- DThe thiocyanate ion is converted into volatile hydrogen sulphide and hydrogen cyanide gases during fusion.
Correct answer
C. The initially formed sodium thiocyanate decomposes to yield sodium cyanide and sodium sulphide.
Step-by-step solution
In Lassaigne's test for an organic compound containing both nitrogen and sulphur, sodium thiocyanate is initially formed during fusion. Na + C + N + S NaSCN The SCN⁻ ion typically reacts with Fe³⁺ to give a blood-red complex, [Fe(SCN)]²⁺ . However, when an excess of sodium metal is used during the fusion process, the sodium thiocyanate decomposes to form sodium cyanide and sodium sulphide. NaSCN + 2Na NaCN + Na₂S Due to the destruction of SCN⁻ ions in the extract, the blood-red coloration is not observed upon the a