JEE Main 2025 Apr 7 Shift 2, Chemistry Q22: Qualitative and Quantitative Analysis

JEE Main2025Apr 7, Shift 2Chemistry

In Dumas' method 292 mg of an organic compound released 50 mL of nitrogen gas (N $_{2}$ ) at 300 K temperature and 715 mm Hg pressure. The percentage composition of 'N' in the organic compound is _____ % (Nearest integer)

(Aqueous tension at 300 K = 15 mm Hg)

Your answer

Solution

The nitrogen gas collected is moist, so its true (dry) pressure must be corrected for aqueous tension: $P_{N_{2}} = 715 - 15 = 700$ mm Hg $= \frac{700}{760}$ atm.

Using the ideal gas equation, moles of collected gas: $n = \frac{P V}{R T} = \frac{700}{760} \times \frac{50}{1000} \times \frac{1}{0.0821 \times 300}$ .

Since the collected gas is N $_{2}$ (diatomic), moles of nitrogen atoms $n_{N} = 2 n_{N_{2}}$ , so mass of N $= 2 \times n_{N_{2}} \times 14$ g.

$% N = \frac{mass of N}{mass of compound} \times 100 = \frac{700}{760} \times \frac{50}{1000} \times \frac{2 \times 14}{0.0821 \times 300} \times \frac{1000}{292} \times 100 \approx 18%$ .

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JEE Main 2025 Apr 7 Shift 2, Chemistry Q22: Qualitative and Quantitative Analysis

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