Question

In Kjeldahl’s method, nitrogen present is estimated as:

• A. $N_2$
• B. $N{H}_3$
• C. $N{O}_2$
• D. None of these

Answer 1

The correct option is B $N{H}_3$

In Kjeldhal's method, the compound containing nitrogen is heated with concentrated sulphuric acid and copper sulphate. Nitrogen in the compound gets converted into ammonium sulphate.
$\text{Organic compound}+H_{2}S{O}_4⟶(N{H}_4{)}_{2}S{O}_4$

The resulting acid mixture is then heated with an excess of sodium hydroxide to produce sodium sulphate and ammonia.

$(N{H}_4{)}_{2}S{O}_4+2NaOH\to N{a}_{2}S{O}_4+2N{H}_3+2H_{2}O$

The liberated ammonia gas is absorbed in a standard solution of known volume of excess sulphuric acid.
The amount of ammonia produced is determined by estimating the amount of sulphuric acid consumed in the reaction.
The amount of unreacted sulphuric acid left after the absorption of ammonia is estimated by titrating it with a standard alkali solution.
Thus, nitrogen present in the organic compound is estimated as $N{H}_3$ in Kjeldahl's method.