Chemistry
posted by Elizabeth .
I don't know exactly how to start this question:
A sample gas contains 2.95 x 10e24 molecules. The sample is 21.0% oxygen. Calculate volume of oxygen in liters assuming oxygen has a density of 1.308 g/L.
Please help me how to do this. I have been stuck and still trying to figure this one out.

figure moles of gas first; moles=2.95E24/avag number
then moles O2=molestotal*.21
then mass 02=molesO2*32grams/mole
then volume=massO2/density 
Okay. Please check. If you can please show me how its done when you put it together. I have it scattered so I was a bit stuck when I tried to do each step. I know dimensional analysis allows the cross cancelling when you do it on paper and its hard to see whats cancelled in each step on the computer. Thank you so much.
2.95E24/6.02E23=4.90 mol (g)
(4.90mol O)(0.21 O)=1.029 mol O
2(15.9994)=31.9988 g/mol O:
(1.029 mol O)(31.9988 g/mol)=32.9267652g
31.9988g/1.308L=24.46 L 
Why don't you put it together on paper so you can see what cancels?