Q15 / 75 · JEE Main 2025 (3 Apr Shift 2) · Chemistry

In Dumas' method for estimation of nitrogen 0.4 g of an organic compound gave 60 mL of nitrogen collected at 300 K temperature and 715 mm Hg pressure. The percentage composition of nitrogen in the compound is
(Given : Aqueous tension at $300 \mathrm{~K}=15 \mathrm{~mm} \mathrm{Hg}$)

  • Correct answer
    A
    $15.71 \%$
  • B
    $20.95 \%$
  • C
    $17.46 \%$
  • D
    $7.85 \%$

Solution

$\text { Pressure of } \begin{aligned}<br />\mathrm{N}_2 \text { gas evolved } & =715-15 \\<br>& =700 \mathrm{~mm} \mathrm{Hg} \\<br>& =\frac{700}{760} \mathrm{~atm}.<br />\end{aligned}$
$\begin{aligned}<br />\therefore \text { Mole of } \mathrm{N}_2 \text { evolved } & =\frac{\mathrm{PV}}{\mathrm{RT}} \\<br>& =\frac{700 \times 60 \times 10^{-3}}{760 \times 0.0821 \times 300} \\<br>& =0.0022 \mathrm{~mole}<br />\end{aligned}$
$\therefore \mathrm{wt}. \%$ of nitrogen in compound
$\begin{aligned}<br />& =\frac{\text { wt. of nitrogen }}{\text { wt. of compound }} \times 100 \\<br>& =\frac{0.063}{0.4} \times 100 \\<br>& =15.71 \%<br />\end{aligned}$

Hence, the correct answer is option: 'A'.

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