Estimation of Nitrogen: There are two methods for the estimation of nitrogen (1) Dumas method and (2) Kjedahl's method.
(1) Duma's method: A known mass of compound is heated with copper oxide (CuO) in an atmosphere 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)+(2x+(y)/(2))Cu.`
The gaseous mixture is passed over a heated copper gauze which converts traces of nitrogen oxides formed of `N_(2)` .The gaseous mixture is collected over an aqueous solution of KOH which absorbs `CO_(2)` and nitrogen is collected in the upper part of the graduated tube.
(2) 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)` (25 ml) , 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 passes 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 amound of acid used against `NH_(3)` can thus be known and from this the percentage of nitogen 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)`
(3) This method is not applicable to compounds containing N in nitro and azo groups,and N persent in the ring (e.g., pyridine as N of these conpounds does not change to `(NH_(4))_(2)SO_(4)` (ammonium sulphate ) under these reaction condition.
0.002 gm of an organic compound was treated according to Kjeldahl's method .`0.2 xx 10^(-4)` mol of `H_(2)SO_(4)` was required to neutralise `NH_(3)` . Calculated the percentage of N.

Options

A. 50
B. 28
C. 70
D. 4

Answer

B