JEE Main · 2026 · 22 Jan 2026 · Shift 2 · Practical and Analytical Chemistry

In Kjeldahl estimation the ammonia liberated from the nitrogen of the sample is absorbed in a known amount of acid, so the moles of acidic hydrogen neutralised equal the moles of nitrogen in the compound. The acid provided is $15\text{mL}$ of $1\mathrm{M}{\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$, that is $0.015\text{mol}\times 2=0.030$ mol of replaceable ${\mathrm{H}}^{+}$, which fixes $0.030$ mol of $\mathrm{N}{\mathrm{H}}_3$ and hence $0.030$ mol of nitrogen. The mass of nitrogen is $0.030\times 14=0.42$ g contained in the $1$ g sample, so the percentage of nitrogen is $\frac{0.42}{1}\times 100=42\%$.