# Help with mass and molar concentrations

1. Feb 24, 2011

### ana111790

1. The problem statement, all variables and given/known data
At 37 ° C and 1.0 atm of pressure, air is 21.2% O2, 0.15 % CO2 and 78.65 % N2. Determine the mass and molar concentrations of each of the gases in the air.

2. Relevant equations
Molecular weight of O2=.032kg/L
Molecular weight of N2=.028kg/L
Molecular weight of CO2 = .044kg/L
PV=nRT

3. The attempt at a solution
I don't know how to start because I am not given V, mass, or number of moles (so the ideal gas law isn't useful). I am also not sure if the percentages given are in terms of mass/volume/number of moles so I am very confused. How should I approach this problem?

2. Feb 25, 2011

### Staff: Mentor

Assume V = 1L. Alternatively derive formula for concentration using V as a variable - in the end it will miraculously cancel out. These are not mass percentages (think what Avogadro's law tells you about volume/moles).

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