JEE Main · 2025 · 03 Apr 2025 · Shift 2 · Practical and Analytical Chemistry

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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 K = 15 mm Hg

)

(A) $15.71%$ ✓ Correct
(B) $20.95%$
(C) $17.46%$
(D) $7.85%$

Answer: (A)

Solution

The nitrogen is collected over water, so its partial pressure is the measured value less the aqueous tension,

715 - 15 = 700 mm Hg = 700/760 atm

. With

V = 0.060 L

and

T = 300 K

, the amount of nitrogen is

n = \frac{P V}{R T} = \frac{( 700/760 ) ( 0.060 )}{0.0821 \times 300} = 2.24 \times 1 0^{- 3} mol

, whose mass is

2.24 \times 1 0^{- 3} \times 28 = 0.0628 g

. The percentage of nitrogen is

\frac{0.0628}{0.4} \times 100 = 15.71%

JEE Main · 2025 · 03 Apr 2025 · Shift 2 · Single correct option

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JEE Main · 2025 · 03 Apr 2025 · Shift 2 · Practical and Analytical Chemistry

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