The various gas laws can be used to describe air, which is a mixture of gases. I
ID: 979061 • Letter: T
Question
The various gas laws can be used to describe air, which is a mixture of gases. In some cases, these laws have direct application to the air that we breathe. Typically, when a person coughs, he or she first inhales about 2.20 L of air at 1.00 atm and 25 degree C. The epiglottis and the vocal cords then shut, trapping the air in the lungs, where it is warmed to 37 degree C and compressed to a volume of about 1.70 L by the action of the diaphragm and chest muscles. The sudden opening of the epiglottis and vocal cords releases this air explosively. Just prior to this release, what is the approximate pressure of the gas inside lungs? Express your answer numerically in atmospheres. Helium-oxygen are used by drivers to avoid the bends and used in medical to treat some respiratory ailments. What percent (by moles) of He is present in a helium-oxygen having a density of 0.518 g/L at 25 degree C and mmHg? Express your answer numerically as a percentage.Explanation / Answer
p*V=n*R*T
p*V=(mass/molar mass)*R*T
p*molar mass=(mass/V)*R*T
p*molar mass=density*R*T
p= 721 mm Hg= 721/760 atm = 0.949 atm
density = 0.518 g/L
R = 0.0821 atm-L/mol-K
T = 25 oC = (25+ 273) K = 298 K
p*molar mass=density*R*T
0.949*molar mass = 0.518 * 0.0821 * 298
molar mass = 13.34 g/mol
Let percentage of Oxygen be x and that of He be 100 -x
Molar mass of O2 = 32 g/mol
Molar mass of He = 4 g/mol
Net molar mass = {x*32 + (100-x)*2 } /100
13.34 *100 = 32*x + 200 - 2*x
30*x = 1134
x = 37.8 %
Percentage of He = 100 - 37.8 = 62.2 %
Answer: 62.2 %
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