Question
For the estimation of nitrogen, $$1.4 g$$ of an organic compound was digested by Kjeldahl method and the evolved ammonia was absorbed in $$60\,{\text{mL}}\,{\text{of}}\,\frac{M}{{10}}$$ sulphuric acid. The unreacted acid required $$20\,{\text{mL}}\,{\text{of}}\,\frac{M}{{10}}$$ sodium hydroxide for complete neutralization. The percentage of nitrogen in the compound is:
A.
$$6\% $$
B.
$$10\% $$
C.
$$3\% $$
D.
$$5\% $$
Answer :
$$10\% $$
Solution :
$$\eqalign{
& \% \,{\text{of}}\,N = \frac{{1.4 \times {\text{meq}}{\text{. of acid}}}}{{{\text{mass of organic compound}}}} \cr
& {\text{meg}}{\text{.}}\,{\text{of}}\,{H_2}S{O_4} = 60 \times \frac{M}{{10}} \times 2 = 12 \cr
& {\text{meg}}{\text{.}}\,{\text{of}}\,NaOH = 20 \times \frac{M}{{10}} = 2 \cr
& \therefore \,\,{\text{meg}}{\text{.}}\,{\text{of}}\,{\text{acid}}\,{\text{consumed}} = 12 - 2 = 10 \cr
& \therefore \,\,\% \,{\text{of}}\,N = \frac{{1.4 \times 10}}{{1.4}} = 10\% \cr} $$