Question

The Kjeldahl' s method for the estimation of nitrogen can be used to estimate the amount of nitrogen in which one of the following compounds?

• A.
• B.
• C.
• D.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Kjeldahl's method is used to estimate nitrogen by converting it into ammonium sulfate via digestion with concentrated $H_2SO_4$.
However, this method has limitations based on the structural environment of the nitrogen atom in the organic molecule.
Step 2: Detailed Explanation:
1. Limitations of Kjeldahl's Method:
The method fails for compounds where nitrogen is:
- Part of a nitro group ($-NO_2$).
- Part of an azo group ($-N=N-$).
- Present in a ring structure (heterocyclic compounds like pyridine or quinoline).
In these cases, nitrogen is not quantitatively converted into ammonium sulfate during the digestion process.

2. Analyzing the Options:
- Nitrobenzene: Contains nitrogen in a nitro group. Not suitable.
- Pyridine: Nitrogen is part of the aromatic ring. Not suitable.
- Aniline: Nitrogen is in an amino group ($-NH_2$) attached to a ring. This nitrogen is easily converted to $(NH_4)_2SO_4$. Suitable.
- Azobenzene: Contains nitrogen in an azo group. Not suitable.
Step 3: Final Answer:
Kjeldahl's method is suitable for aniline.