Differentiate between the principle of estimation of nitrogen in an organic compound by (i) Dumas method and (ii) Kjeldahl’s method.

Explanation

(i) In Dumas method, a known mass of the organic compound is heated with excess of CuO in an atmosphere of `CO_(2)`, when nitrogen of the organic compound is converted into `N_(2)` gas. The volume of `N_(2)` thus obtained is converted into NTP and the percentage of nitrogen determined by applying the equation.
`%N = (28)/(22400) xx ("Vol. of " N_(2) " at NTP")/("Mass of the substance taken")`
(ii) In Kjeldahl's method, a known mass of the organic substance is digested (heated) with conc. `H_(2)SO_(4)` in presence of `K_(2)SO_(4)` (raises the b.p. of `H_(2)SO_(4)`) and little `CuSO_(4)` or Hg (catalyst) in a long necked flask called Kjeldahl's flask when nitrogen in the organic compound is quantitatively converted into `(NH_(4))_(2)SO_(4). (NH_(4))_(2)SO_(4)` thus obtained is boiled with excess of NaOH solution to liberate `NH_(3)` gas which is absorbed in a known excess of a standard acid such as `H_(2)SO_(4)` or HCl.
The volume of acid unused is formed by titration against a standard alkali solution. From the volume of the acid used, the percentage of nitrogen is determined by applying the equation,
`%N = (1.4 xx "Molarity of the acid" xx "Basicity of the acid" xx "Vol. of the acid used")/("Mass of the substance taken")`