KJELDAHL’ S METHOD: A known mass of organic compound is heated with conc. H2SO4 in presence of K2SO4 and little CuSO4 or Hg in a long necked flask called Kjeldahl’ 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 absorbed in a known excess of a standard acid such as H2SO4 or HCl.
The vol of acid unused is found by titration against a standard alkali solution. From the vol of the acid used, the percentage of nitrogen is determined by applying the equation,
% N = 1.4 x Molarity of the acid x Basicity of the acid x Vol of the acid used
Mass of the substance taken Halogens Carius method:
A known mass of an organic compound is heated with fuming nitric acid in the presence of silver nitrate contained in a hard glass test tube known as carius tube in a furnace. Carbon and hydrogen present in the compound are oxidized to carbon dioxide and water. The halogen present forms the corresponding silver halide. It is filtered, dried, and weighed.
Let the mass of the organic compound taken = m g Mass of AgX formed = m1 g 1 mol of AgX contains 1 mol of of X Mass of halogen in m1 g of AgX
= at mass of X xm1 g Molecular mass of AgX
% of halogen
= at mass of X xm 1 g x 100 % Molecular mass of AgX x m