In: Chemistry
Helium-oxygen mixtures are used by divers to avoid the bends and are used in medicine to treat some respiratory ailments. What percent (by moles) of He is present in a helium-oxygen mixture having a density of 0.508 g/L at 25 ∘C and 721 mmHg?
Express your answer numerically as a percentage.
PV = nRT
P = 721/760 = 0.9486atm
R = 0.0821L-atm/mole-K
T = 25+273 = 298K
V =1L
PV = nRT
n = PV/RT
= 0.9486*1/0.0821*298 = 0.0387moles
find no of moles of helium using molar masses
0.508 = X*4g/mole of He + (0.0387-X)*32g/mole of O2
X = 0.026
X = 0.026 moles of He
He% = no of moles of He*100/total no of moles
=
0.0262*100/0.0387 = 67.7%