Question

$29.5$ 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 the acid required $15$ ml of $0.1$ M NaOH solution for complete neutralization. The percentage of nitrogen in the compound is:

• A. $59.0$
• B. $47.4$
• C. $23.7$
• D. $29.5$

Answer 1

The correct option is C $23.7$

Moles of $HCl$ reacting with ammonia $=$ moles of $HCl$ absorbed

$=$ moles of $NaOH$ solution required

$=(20\times 0.1\times {10}^{-3})-(15\times 0.1\times l{0}^{-3})$

$=$ moles of $N{H}_3$ evolved

$=$ moles of nitrogen in organic compound
Weight of nitrogen in organic compound $=0.5\times {10}^{-3}\times 14=7\times {10}^{-3}g$

$\%$ nitrogen $=\frac{7\times {10}^{-3}}{29.5\times {10}^{-3}}\times 100=23.7$ %

Option C is correct.