29.5 mg of an organic compound containing nitrogen was digested according to Kjeldahl's method and the evolved ammonia was absorbed in 20 ml of 0.1 M HCl solution. The excess of acid required 15 ml of 0.1 M NaOH solution for complete neutralisation. The percentage of nitrogen in the compound is:
Correct option is C. 23.7
millimoles of $$HCl$$ observed $$=20\times 0.1=2$$
millimoles of $$NaOH=15\times 0.1=1.5$$
Moles of $$HCl$$ reacting with Ammonia=moles of HCl absorbed$$-$$Moles of $$NaOH$$ solution required$$=2-1.5=0.5$$
millimoles of $$NH_{3}=0.5$$
Milligrams of $$N$$ in $$NH_{3}=0.5\times 14=7mg$$
$$\% \ of\ N=\cfrac{7}{29.5}\times 100=23.7 \% $$
$$\mathbf{Hence\ the\ correct\ answer\ is\ option\ (C).}$$