Question

In the estimation of nitrogen by Dumas method $1.18g$ of an organic compound 224ml of ${N_2}$ at NTP , the percentage of nitrogen in the compound is about:
A. 20.0
B. 11.8
C. 47.5
D. 23.72$$

Answer 1

Hint: The analysis of total nitrogen in an organic compound can be carried out using Dumas method. This involves a total combustion of the compound under oxygen. The gases produced are reduced by copper and then dried, while the carbon dioxide is trapped. Then nitrogen is then quantified using a universal detector.

Complete Step by step answer: the Dumas method in analytical method for quantitative determination of nitrogen in a chemical substance based on a method described by Jean-Baptiste Dumas in 1831.
This method has three steps: combustion, reduction and separation and detection.
In the combustion process, organic substances are heated at high temperatures and combustion occurs in the presence of oxygen, and this leads to substances such as carbon dioxide, water, and nitrogen oxides.
In the reduction and separation step, the gas mixture passed over hot copper to remove any oxygen and convert nitrogen oxides to nitrogen. The sample is then passed through traps that remove water and carbon dioxide.
The mixture of gas collected over $KOH$ , and here $KOH$ absorbs $C{O_2}$ and forms potassium carbonate.
the reaction occur there are:
$
  C + 2CuO \to C{O_2} + 2Cu \\
  2H + CuO \to {H_2}O + Cu \\
 $
 $N + CuO \to {N_2} + $ Oxides of nitrogen
Oxides of nitrogen $ + Cu \to {N_2} + CuO$
Next is detection step-
Here the volume of nitrogen gas given as $224ml$, volume of $1mole$ of gas is $22400ml$ ,so mole of nitrogen gas will be $\dfrac{{224}}{{22400}} = 0.01$
Now, the mass of nitrogen gas evolved will be $0.01 \times 28 = 0.28gm$ . This means an organic compound contains $0.28gm$ of nitrogen.
Percentage of nitrogen in the compound will be $ = \dfrac{{0.28}}{{1.18}} \times 100 = 23.72$

Hence the correct option D.

Note: The Dumas method has the advantage of being easy to use. It is also considerably faster than the Kjeldahl method. It takes less time than the kjeldahl method. It also does not make use of toxic chemicals. Or eco friendly catalyst.