Question

Part A: What mass of carbon dioxide is present in 1.00 m3 of dry air at a temperature of 19?C and a pressure of 651torr? Express your answer with the appropriate units.

Part B: Calculate the mass percentage of oxygen in dry air. Express your answer with the appropriate units.

If you could explain how you got your answer that would be great! Thank you!

Here is given info:

Air is a mixture of several gases. The 10 most abundant of these gases are listed here along with their mole fractions and molar masses.

Component	Mole fraction	Molar mass (g/mol)
Nitrogen	0.78084	28.013
Oxygen	0.20948	31.998
Argon	0.00934	39.948
Carbon dioxide	0.000375	44.0099
Neon	0.00001818	20.183
Helium	0.00000524	4.003
Methane	0.000002	16.043
Krypton	0.00000114	83.80
Hydrogen	0.0000005	2.0159
Nitrous oxide	0.0000005	44.0128

Answer 1

Part A

These are the proportions

Nitrogen - 78.09 % - Oxygen - 20.95% - Argon - .93% - - Carbon Dioxide - .03% Methane -.04% Neon - .0018% - Helium - .0005% Krypton - .0001% - Hydrogen Nitrous Oxide - negligible amount

You get the atomic weights of the above and then the number of moles and work out with the percentages.

atomic/molecular weights:

O2 32.00
N2 28.02
CO2: 44.01
H2: 2.02
Ar2 39.04
Ne2 21.08
He2 4.00
K 83.8

You only need to consider O2 N2 CO2 and Ar2 as the others are trace amouts.

kg/kmol:
O2 32.00
N2 28.02
CO2: 44.01
Ar2 39.04

fraction of gases:
02 0.2095
N2 0.7809
CO2 0.0003
Ar2 0.0093

Molecular mass
02 6.704
N2 21.88
CO2 0.013
Ar2 0.373

Total = 28.97

? = p / (R T)

where

p = pressure (kPa)

R = 286.9 = individual gas constant (J/kg degK)

T = absolute temperature (degK)

pressure 675 torr = 89.993 kPa and T = 273 + 23 = 296 degK
? = (89.993 kPa) / ((286.9 J/kg degK) (296 degK))

= 1.0597 kg/m3 air

(0.013/28.97)*1.0597 = 0.0004755 kg in 1.00 m^3 = 0.4755 grams per 1.00 m^3

Part B

23.1%

add up the first few (Mole fraction x Molar Mass), you'll see the molar mass of dry air is ~29
divide oxygen's (Mole fraction x Molar Mass) / 29 and you'll get .231135...

so, to 3 sig figs: oxygen is 23.1% by mass in dry air

Source(s):I did this problem in Mastering Chemistry and got the correct answer