Question

${N_2}$ is estimated in organic compound by
A) Duma’s method
B) Carius method
C) Lassaigne’s method
D) None of these

Answer 1

Hint: For the estimation of nitrogen in the organic compound, there is a need for reactivity for the products formed in the reaction. One can think about the reagents used in each option method and decide which can give the specific reactivity to the nitrogen and estimate it. The copper oxide reagent can be used for the estimation of a nitrogen molecule.

Complete step by step answer:
1) First of all we will discuss the concept of estimation of nitrogen. The estimation of nitrogen in an organic compound is the amount of nitrogen in that organic molecule.
2) So, how do we do that. Duma’s method is generally used for the estimation of the nitrogen molecule. The steps that are used in this method are as follows.
3) In the first step of this method the unknown organic compound is reacted with the copper oxide in presence of heat which gives the products as below,
$O.C. - N\xrightarrow[{CuO}]{{Heat}}C{O_2} + {H_2}O + {N_2} + Cu$
In the above reaction when the unknown organic compound containing the nitrogen is reacted with the copper oxide in presence of heat it yields the products as carbon dioxide, water, nitrogen molecule, and copper.
4) Now as the products are formed and how do we estimate the nitrogen molecules. We can do this by reacting the products with the solution of the potassium hydroxide i.e. ${\text{KOH}}$.
5) When we treat the products with the potassium hydroxide the products $C{O_2}$, ${H_2}O$, ${\text{Cu}}$ react with the ${\text{KOH}}$ but the nitrogen doesn’t react with potassium hydroxide which leaves the free nitrogen in the solution. Hence, as the nitrogen is free in the product we can estimate it by measuring the volume of nitrogen and calculating the percentage composition.
And hence option A is the correct answer.

Note:
The Duma’s method is performed at a very high temperature which is around ${\text{975K}}$. During the process, if any amount of nitrogen gets oxidized then it is again converted back to free nitrogen by passing it over a hot copper gauze.