Question:
In the estimation of nitrogen by Kjeldahl's method, the ammonia produced by \(2.0\,\text{g}\) of an organic compound was completely neutralized by \(20\,\text{mL}\) of \(2\,\text{M}\) sulphuric acid. The percentage of nitrogen in the compound is
In the estimation of nitrogen by Kjeldahl's method, the ammonia produced by \(2.0\,\text{g}\) of an organic compound was completely neutralized by \(20\,\text{mL}\) of \(2\,\text{M}\) sulphuric acid. The percentage of nitrogen in the compound is
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In Kjeldahl's method,
\[
\boxed{
\mathrm{H_2SO_4+2NH_3\rightarrow(NH_4)_2SO_4}.
}
\]
Always calculate moles of ammonia first, then convert them into mass of nitrogen.
Updated On: Jul 18, 2026
- \(56\)
- \(28\)
- \(36\)
- \(46\)
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The Correct Option is A
Solution and Explanation
Step 1: Calculate the moles of sulphuric acid.
\[
n(\mathrm{H_2SO_4})
=
MV
=
2\times0.020
=
0.040\ \text{mol}.
\]
Step 2: Find the moles of ammonia. The reaction is \[ \mathrm{H_2SO_4+2NH_3 \rightarrow (NH_4)_2SO_4.} \] Hence, \[ n(\mathrm{NH_3}) = 2\times0.040 = 0.080\ \text{mol}. \] Since each mole of ammonia contains one mole of nitrogen, \[ n(\mathrm{N})=0.080\ \text{mol}. \] Mass of nitrogen is \[ 0.080\times14 = 1.12\ \text{g}. \]
Step 3: Calculate the percentage of nitrogen. \[ \%\mathrm{N} = \frac{1.12}{2.0}\times100 = 56\%. \] Hence, \[ \boxed{56\%.} \] Therefore, the correct option is \(\boxed{(A)}\).
Step 2: Find the moles of ammonia. The reaction is \[ \mathrm{H_2SO_4+2NH_3 \rightarrow (NH_4)_2SO_4.} \] Hence, \[ n(\mathrm{NH_3}) = 2\times0.040 = 0.080\ \text{mol}. \] Since each mole of ammonia contains one mole of nitrogen, \[ n(\mathrm{N})=0.080\ \text{mol}. \] Mass of nitrogen is \[ 0.080\times14 = 1.12\ \text{g}. \]
Step 3: Calculate the percentage of nitrogen. \[ \%\mathrm{N} = \frac{1.12}{2.0}\times100 = 56\%. \] Hence, \[ \boxed{56\%.} \] Therefore, the correct option is \(\boxed{(A)}\).
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