In the Dumas method for the estimation of nitrogen, 0.28 g of an organic compound gave 89.6 mL of nitrogen gas collected over water at 273 K and a total pressure of 400 mm Hg . If the aqueous tension at 273 K is 20 mm Hg , the percentage of nitrogen in the compound is ________. (Given: Molar mass of N ₂ is 28 g mol ⁻¹ , Molar volume of N ₂ at STP is 22400 mL , Standard pressure is 760 mm Hg )

Step-by-step solution

Pressure of dry N ₂ gas: P_ dry = P_ total - Aqueous tension = 400 - 20 = 380 mm Hg Since the temperature is 273 K (which is standard temperature), we apply Boyle's Law to find the volume at standard pressure ( 760 mm Hg ): V_ STP = P_ dry V_ obs 760 = 380 89.6 760 = 44.8 mL Moles of N ₂ gas at STP: n = 44.8 22400 = 0.002 mol Mass of N ₂ gas: W = 0.002 28 = 0.056 g Percentage of nitrogen in the compound: % N = 0.056 0.28 100 = 20 % Answer: 20