NCERT/CBSE CHEMISTRY CLASS 11 textbook
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CHAPTER TWELVE
ORGANIC CHEMISTRY – SOME BASIC PRINCIPLES AND TECHNIQUES
12.22 Differentiate between the principles of estimation of nitrogen in an organic compound by
(i) Dumas method and (ii) Kjeldahl’s method.
(i) Dumas method: - In this method a known mass of the organic compound is heated with
CuO in an atmosphere of CO2.The nitrogen present in the organic compound is converted
to N2 gas. This N2 gas is collected by the down ward displacement of water. The volume of
the N2 obtained is note and converted to STP. % of N2 present is calculated by the formula
given below.
% of N= (28 ÷22400) x (Vol of N2 at STP ÷ Mass of the organic compd taken) x100
(ii) Kjeldahl’s method. : - In this method a known mass of the organic compound is heated
with conc H2SO4 in the presence of K2SO4 and Hg as catalyst in a Kjeldahl’s
flask that has a long neck. The N2 present in the organic compound is converted to
ammonium sulphate. This ammonium sulphate, which is obtained, is boiled with NaOH. The
NH3 gas, which is liberated, is passed through a standardized solution of H2SO4.The
volume of the unused acid is found out by titration with standard KOH or NaOH solution.
The % of N2 is calculated from the volume of the acid used from the formula given below.
1.4 x Molarity of acid x basicity of the acid x vol of the acid
% 0f N =
_________________________________________________
Mass of the organic compd taken
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