Air is a mixture of 21% oxygen gas and 79% nitrogen gas. Calculate the average molar mass of a mixture of air. I’m very lost, I thought I was supposed to use mole fraction but it does not get me anywhere, due to not having the total amount of moles. Maybe it has to do with finding pressure?
Here are formulas that I know of:
MM = DRT/P
- MM is molar mass
- D is density
- R is ideal gas constant
- T is temperature in Kelvin
- P is pressure
PV = nRT
- V is volume
- n is moles
Please help, thank you.

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