JEE Main 2025 Apr 4 Shift 1, Chemistry Q21: Qualitative and Quantitative Analysis

JEE Main2025Apr 4, Shift 1Chemistry

In Dumas' method for estimation of nitrogen 1g of an organic compound gave 150 mL of nitrogen collected at 300K temperature and 900 mm Hg pressure. The percentage composition of nitrogen in the compound is _____ % (nearest integer).

(Aqueous tension at 300 K = 15 mm Hg)

Your answer

Solution

Correct the gas pressure for aqueous tension: $P_{N_{2}} = 900 - 15 = 885$ mm Hg $= \frac{885}{760}$ atm.

Using ideal-gas law $n = \frac{P V}{R T}$ with $V = 0.150$ L, $T = 300$ K, $R = 0.0821$ L atm K $^{- 1}$ mol $^{- 1}$ :

$n_{N_{2}} = \frac{( 885/760 ) ( 0.150 )}{( 0.0821 ) ( 300 )} \approx 7.10 \times 1 0^{- 3}$ mol.

Mass of nitrogen $= n \times 28 = 7.10 \times 1 0^{- 3} \times 28 \approx 0.1988$ g.

$% N = \frac{0.1988}{1} \times 100 \approx 19.88%$ .

Nearest integer = 20.

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JEE Main 2025 Apr 4 Shift 1, Chemistry Q21: Qualitative and Quantitative Analysis

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