Estimation of nitrogen: There are two methods for the estimation of nitrogen (i) Dumas method and (ii) Kjedahl's method.
i. Dumas method: A known mass of compound is heated with copper oxide (CuO) in an atomsphere of `CO_(2)`, which gives free nitrogen along with `CO_(2) and H_(2)O`
`C_(x)H_(y)N_(z) + (2x + y//2) CuO rarr xCO_(2) + y//2 (H_(2)O) + z//2 (N_(2)) + (2x + y//2) CU`
The gaseous mixture is passed over a heated copper gauze which converts traces of nitrogen oxides formed to `N_(2)`. The gaeous mixture is collected over an aqueous solution of KOH which absorbs `CO_(2)`, and nitrogen is callected in the upper part of the graduated tube.
ii. Kjeldahl's method: A known mass of organic compound (0.5 gm) is mixed with `K_(2)SO_(4)` (10 gm) and `CuSO_(4)`. (1.0 gm) or a drop of mercury (Hg) and conc. `H_(2)SO_(4)` (25ml), and heated in Kjeldahl's flask. `CuSO_(4)` or Hg acts as a catalyst, while `K_(2)SO_(4)` raises the boiling point of `H_(2)SO_(4)`. The nitrogen in the organic compound is quantitatively converted to ammonium sulphate. The resulting mixture is then distilled with excess of NaOH solution and the `NH_(3)` evolved is passed into a known but excess volume of standard HCl or `H_(2)SO_(4)`. The acid left unused is estimated by titration with some standard alkali. The amount of acid used against `NH_(3)` can be thus be known and from this the percentage of nitrogen is calculated.
(a) `C + H + S underset(H_(2)SO_(4))overset("conc.")rarr CO_(2) + H_(2)O + SO_(2)`
(b) `N underset(H_(2)SO_(4))overset("conc.")rarr (NH_(4))_(2)SO_(4)`
(c) `(NH_(4))_(2) SO_(4) + 2NaOH rarr Na_(2)SO_(4) + 2NH_(3) + 2H_(2)O`
(d) `2NH_(3) + H_(2)SO_(4) rarr (NH_(4))_(2) SO_(4)`
(iii) This method is not applicable to compounds containing N in intro and azo groups, and N present in the ring (e.g., pyridine) as N of these compounds does not change to `(NH_(4))_(2)SO_(4)` (ammonium sulphate) under these reaction conditions
0.20gm of an organic compound gave 82.1 ml of nitrogen collected at 300K and 775mm pressure in Dumas method. Calculate the percentage of nitrogen in the compound. (Vapour pressure of water or aqueous tension of water at 300K is 15mm.

Options

A. `31.11`
B. `15.56`
C. `28.0`
D. `31.72`

Answer

A