Question

29.5 mg of an organic compound containing nitrogen was digested according to Kjeldahr'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. Determine the percentage of nitrogen in the compound.

• A. $23.7$
• B. $25.4$
• C. $21.4$
• D. $29.5$

Answer 1

Answer: (A)

Moles of HCI reacting with ammonia = (moles of $HCI$ 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. = $\frac{7\times {10}^{-3}}{29.5\times {10}^{-3}}=23.7$%