how many oxygen molecules in a cubic metre of air.?

Question

Lets test highschool chemistry. Its been a while for me.

Lets say for a given 1.2kg per M3 density

Answer 1

5.323x10^24

6.022x10^23 is Avogadro's (I think that's how it's spelled, it's been a long time for me too) number which is molecules per gram mole. There are 453.6 gmols in a lbmol. There are 379.5 standard cubic feet of gas per lbmol (this is the critical number that allows me to answer the question, but I could have used the 22.414 liters per gmol at a different set of standard conditions). The standard conditions for the 379.5 number are 1 atmosphere and 60° F - let's just assume that these are the conditions since you did not specify. Since there are 35.3 ft3 per m3, and bone dry air is 20.95% oxygen by volume, then the math is fairly straight forward.
0.2095*35.3/379.5*453.6*6.022x10^23
which gives:
5.323x10^24 oxygen molecules per cubic metre of dry air at 1 atmosphere and 60°F.

Answer 2

How Many Oxygen In Air

Answer 3

The temperature and pressure are required to answer this, otherwise can't be done.

We can assume STP for the moment (zero celsius and 1 atm.)

In this case there is a mole of gas in 22.4 liters. There are 1,000 liters in a cubic meter. So divide 1,000 by 22.4 and that will give you moles in a cubic meter. Multiply the moles by Avogadro's number (6.02 x 10 E23) and that will give you molecules of air. Oxygen is about 20% of air, so mulitply again.