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

In Dumas' method for estimation of nitrogen, 0.5 gram 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 (Aqueous tension at $300 \mathrm{~K}=15 \mathrm{~mm} \mathrm{Hg})$ is

  • A
    1.257
  • B
    20.87
  • C
    18.67
  • Correct answer
    D
    12.57

Solution

$\begin{aligned} & \text { Pressure of } \mathrm{N}_2 \text { gas }=(715-15) \\ & \begin{array}{l}=700 \mathrm{mmHg} \\ \mathrm{n}_{\mathrm{N}_2}=\frac{\mathrm{PV}}{\mathrm{RT}} \\ \mathrm{n}_{\mathrm{N}_2}=\frac{700 \times 60 \times 10^{-3}}{760 \times 0.0821 \times 300} \\ \quad=2.24 \times 10^{-3} \mathrm{~mol}\end{array} \\ & \begin{array}{r}\text { Mass of } \mathrm{N}_2=2.24 \times 10^{-3} \times 28 \mathrm{~g} \\ \quad=0.06272 \mathrm{~g}\end{array} \\ & \begin{array}{r}\% \mathrm{~N}_2=\frac{0.06272}{0.5} \times 100 \simeq 12.57\end{array}\end{aligned}$

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

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