Question

Dumas and Kjeldahl's methods are used for the quantitative estimation of:

• A. Phophorous
• B. Halogens and Sulphur
• C. Nitrogen
• D. All of the above.

Answer 1

The correct option is C Nitrogen

Nitrogen can be estimated by either of the two methods:
1. Dumas' method
2. Kjeldahl's method
Kjeldahl's method:
The compound containing nitrogen is heated with concentrated sulphuric acid and copper sulphate. Nitrogen in the compound gets converted into ammonium sulphate.
The reaction is :
$\text{Organic compound}+H_{2}S{O}_4\to (N{H}_4{)}_{2}S{O}_4$
The resulting acid mixture is then heated with an excess of sodium hydroxide
$(N{H}_4{)}_{2}S{O}_4\stackrel{2NaOH}{⟶}N{a}_{2}S{O}_4+2N{H}_3+2H_{2}O$

The liberated ammonia gas is absorbed in a standard solution of excess sulphuric acid.
$2N{H}_3+H_{2}S{O}_4⟶(N{H}_4{)}_{2}S{O}_4$

Hence, option C is correct.