1.) The density of air at STP is 1.29g/L. If your stoppered \"250mL\" flask cont
ID: 799380 • Letter: 1
Question
1.) The density of air at STP is 1.29g/L. If your stoppered "250mL" flask contains 242 ml of water ( also the volume of air it would contain), calculate the mass of air in the flask under STP.
2.) What would be the density of air under 20degree C and 720mm Hg? ( Hint : gas density is proportional to P and inversely proportional to T).
3.) Estimate the avearge molar mass of air assumig it contains 80% N2 and 20% O2.
4.) Calculate the R value based on density and the avarge molar mass of air
a.) under STP
b.) under 20degree C and 720mm Hg
Explanation / Answer
1.assuming water doe not evaporate inside the flask
8ml of air is present
mass=1.29*.008=.01gm of air is present
2.P/d= constant
760/1.29=720/d
d=1.22 gm/L
3.moles of N2=.8 O2=.2
M=.8*28+.2*32
M=28.8 g/mol
4.P=dRT/M
1=1.29*273*R/28.8
R=.082atm L/mol k
at 720 and 20 degrees
720/760=1.22*293*R/28.8
R=.0763
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