Given data:
Mass of organic compound (w) = 0.50 g
Volume of nitrogen gas (V1) = 70 mL
Temperature (T1) = 300 K
Total pressure = 715 mm Hg
Aqueous tension = 15 mm Hg
Pressure of dry nitrogen (P1) = 715−15=700 mm Hg
Convert the volume of nitrogen to STP conditions (P0=760 mm Hg, T0=273 K):
Using the combined gas law: T1P1V1=T0P0V0
V0=P0T1P1V1T0=760×300700×70×273≈58.68 mL
At STP, 22400 mL of N2 weighs 28 g.
Mass of N2 collected = 2240028×58.68 g
Percentage of nitrogen = Mass of compoundMass of N2×100
%N=22400×0.5028×58.68×100
%N=11228×58.68=458.68=14.67%
Rounding to the nearest integer, we get 15.