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

Explanation

In Duma.s method, a known mass of the organic compound is heated with CuO in an atmosphere of `CO_2`, when all nitrogen present in the compound evolves quantitatively as `N_2` gas. The percentage of nitrogen is determined by using the following formula:
`%N =( 28 xx "volume of " N_2 "at STP " xx 100 )/( 22400 xx " Mass of the compound taken ")`
In Kjeldahl.s method, the nitrogen present in the compound is quantitatively converted into `(NH_4)_2 SO_4` by heating it with conc. `H_2 SO_4` in the presence of `CuSO_4` (Kjeldahlisation). The Kjeldahlised liquid is heated with excess of NaOH and ammonia thus liberated is absorbed in a known volume of a standard acid. The partly neutralised acid is then back titrated against a standard alkali to determine the amount of NH3 evolved. Following formula is used to estimate the percentage of nitrogen in the compound. Normality of the standard acid
` % N= ( xx "Volume of standard acid used " xx 14 )/( 1000 xx (100)/("Mass of the compound taken "))`