Differentiate between the principle of estimation of nitrogen in an organic compound by 

(i)  Dumas method     

(ii)  Kjeldahl’s method. 

(i) In Dumas method, a known mass of the organic compound is heated with excess of CuO in an atmosphere of CO₂, when nitrogen of the organic compound is converted into N₂ gas. The volume of N₂ thus obtained is converted into NTP and the percentage of nitrogen determined by applying the equation,

%N = 28/22400 × Vol. of N₂ at NTP/Mass of the substance taken × 100

(ii)  In Kjeldahl’s method, a know mass of the organic substance is digested (heated) with conc. H₂SO₄ in presence of K₂SO₄ (raises the b.p. of H₂SO₄) and little CuSO₄ of Hg (catalyst) in a long necked flask called Kjedahl’s flask when  nitrogen present in the organic compound is quantitatively converted into (NH₄)₂SO₄. (NH₄)₂SO₄ thus obtained is boiled with excess of NaOH solution to liberate NH₃ gas which is obsorbed in a known excess of a standard acid such as H₂SO₄ or HCl.                                                   

The volume of acid unused is found by titrataion against a standard alkali solution. Form the volume of the acid used, the percentage of nitrogen is determined by applying the equation,

%N =  (1.4 × Molarity of the acid × Basicity of the acid × Vol. of the acid used)/Mass of the substance taken