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

Answer: (C)

Moles of HCl reacting with ammonia
= (moles of HCl absorbed ) - (moles of NaOH solution required)
$= (20 \times 0.1 \times 10^{-3}) - (15 \times 0.1 \times 10^{-3})$
= moles of $NH_3$ evolved.
= moles of nitrogen in organic compound
$\therefore $ wt. of nitrogen in org. comp $= 0.5 \times 10^{-3} \times 14$
$= 7\times 10^{-3}\,g$
$\% wt = \frac{7\times 10^{-3}}{29.5\times 10^{-3}} = 23.7\%$