Question

$29.5mg$ of an organic compound containing nitrogen was digested according to Kjeldahl’s method and the evolved ammonia was absorbed in $20mL$ of $0.1MHCl$ solution. The excess of the acid required $15mL$ of $0.1MNaOH$ 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 $N{H}_3$ evolved.
= moles of nitrogen in organic compound
$\therefore$ wt. of nitrogen in org. comp $=0.5\times 10^{-3}\times 14$
$=7\times 10^{-3}g$
$\%wt=\frac{7\times 10^{-3}}{29.5\times 10^{-3}}=23.7\%$