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Question

In Kjeldahl's method, nitrogen present is estimated as:

A
$$N_2$$
B
$$NH_2$$
C
$$NO_2$$
D
none of these
Solution
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Correct option is B. $$NH_2$$
Kjeldahl method is a method that is used the quantitatuin estimation of nitrogen conlaining in inorganic substances like $$NH_3/NH_4^+$$, and in organic substances.In kjeldah's method, notrogen is estimated in following steps :
$$Step$$ $$1:$$Degradation: Sample$$+H_SO_4\longrightarrow {(NH_4)}_2SO_4+CO_2+SO_2+H_2O$$
$$Step$$ $$2:$$ Ammonia is liberated : $${(NH_4)}_2SO_4+2NaOH\longrightarrow Na_2SO_4+2H_2O+2NH_3$$
$$Step$$ $$3:$$ Ammonia is captured : $$B{(OH)}_3+H_2O+NH_3\longrightarrow NH^+_4+B{(OH)}_4^-$$
$$Step$$ $$4:$$ Back titration : $$B{(OH)}_3+H_2O+Na_2CO_3\longrightarrow NaHCO_3+NaB{(OH)}_4+CO_2+H_2O$$
Thus in Kjeldahl's method, nitrogen present is estimated as $$NH_2$$.

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