In Dumas’ method for estimation of nitrogen 1 g 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

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Solution

Q.
In Dumas’ method for estimation of nitrogen 1 g 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) [2025]

Ans.
(20)

$Pressure of nitrogen gas (P_{N_{2}}) = Total pressure of gas - aqueous tension$
$= (900 - 15) mmHg = 885 mmHg = \frac{885}{760} atm$

$Volume of nitrogen (V_{N_{2}}) = 150 mL = 0.15 L$

By ideal gas equation, moles of nitrogen $(n_{N_{2}}) = \frac{P_{N_{2}} V_{N_{2}}}{R T}$

$= \frac{\frac{885}{760} \times 0.15}{0.0821 \times 300} = 0.0071 mol$

$Mass of nitrogen (W_{N_{2}}) = n_{N_{2}} \times Molar mass of N_{2}$

$= 0.0071 \times 28 g = 0.1988 g$

Percentage of nitrogen in organic compound $= \frac{Mass of nitrogen in organic compound}{Mass of organic compound} \times 100$

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

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