An organic compound is known to contain 20 % nitrogen by mass. When a certain mass of this compound is analysed using Duma's method, it yields 24.6 mL of nitrogen gas collected over water at 300 K and 775 mmHg pressure. The mass of the organic compound taken for the analysis is ________ mg . (Given: Aqueous tension at 300 K is 15 mmHg , R = 0.082 L atm K ⁻¹ mol ⁻¹ )

Step-by-step solution

Pressure of dry N ₂ gas = P_ total - Aqueous tension P = 775 - 15 = 760 mmHg = 1 atm Using the ideal gas equation, PV = nRT 1 0.0246 = n 0.082 300 n = 0.0246 24.6 = 0.001 mol Mass of nitrogen gas = 0.001 28 = 0.028 g Let the mass of the organic compound be m . Percentage of nitrogen = Mass of N Mass of compound 100 20 = 0.028 m 100 m = 2.8 20 = 0.14 g Mass in mg = 0.14 1000 = 140 mg . Answer: 140