JEE Main · 2025 · 04 Apr 2025 · Shift 1 · Practical and Analytical Chemistry

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In Dumas' method for estimation of nitrogen 1g of an organic compound gave 150 mL of nitrogen collected at 300 K 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

)

Answer: 20

Solution

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

900 - 15 = 885 mm Hg = \frac{885}{760} atm

. From

P V = n R T

n = \frac{( 885/760 ) ( 0.150 )}{( 0.0821 ) ( 300 )} = 7.09 \times 1 0^{- 3} mol

, so the mass of nitrogen is

7.09 \times 1 0^{- 3} \times 28 = 0.199 g

. Its percentage in the

1 g

sample is

\frac{0.199}{1} \times 100 = 19.9%

, i.e.

20%

to the nearest integer.

JEE Main · 2025 · 04 Apr 2025 · Shift 1 · Integer answer

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