In a Kjeldahl estimation, of an organic compound was digested, and the evolved ammonia was absorbed — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Milli-moles of $HCl$ taken = $20 \times 0.1 = 2 \text{ mmol}$. Milli-moles of $NaOH$ used = $15 \times 0.1 = 1.5 \text{ mmol}$. Milli-moles of $HCl$ neutralized by $NH_3$ = $2 - 1.5 = 0.5 \text{ mmol}$. Moles of $NH_3$ = $0.5 \times 10^{-3} \text{ mol}$. Mass of N = $0.5 \times 10^{-3} \times 14 = 7 \text{ mg}$. $\%N = (7 / 29.5) \times 100 \approx 23.7\%$.