Question

Lassaigne?s test is used in qualitative analysis to detect

• A. nitrogen
• B. sulphur
• C. chlorine
• D. all of these

Answer 1

The Correct Option is D

Lassaigne's test is a qualitative analysis technique used to detect the presence of certain elements within organic compounds. Let's discuss the process and how it helps in detecting different elements.

1. Principle of Lassaigne's Test:
   • The test involves converting the elements present in an organic compound into their ionic forms by fusing the organic compound with metallic sodium.
   • The sodium fuses with elements like nitrogen, sulphur, and halogens while forming sodium cyanide, sodium sulphide, and sodium halides, respectively.
2. Detection of Elements:
   • Nitrogen: During the test, nitrogen present in the compound forms sodium cyanide (NaCN), which gives a positive Prussian blue color with iron(II) sulfate followed by the addition of dilute sulphuric acid and ferric ions.
   • Sulphur: Sulphur forms sodium sulphide (Na_2S), which, when treated with sodium nitroprusside, gives a purple color indicating the presence of sulphur.
   • Halogens (e.g., Chlorine): Halogens form sodium halides, such as sodium chloride (NaCl), which can be detected through the addition of silver nitrate after acidifying the sample. A white precipitate of silver chloride confirms the presence of chlorine.
3. Conclusion:

   Given that Lassaigne's test is capable of detecting nitrogen, sulphur, and halogens such as chlorine, the correct answer to the question is all of these. This test is therefore used for the comprehensive detection of these elements within organic compounds.