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How to Calculate the Mass of O2

Molecular oxygen, a compound with the chemical formula O2 is a colorless, tasteless and odorless gas that supports combustion. Air consists of almost 21 percent of oxygen and is essential in the respiratory processes of living organisms. Figuring out the mass of oxygen is the common chemistry class assignment, and is necessary for chemical reaction calculations.

Instructions

Finding Molar Mass
- 1
  Find the atomic weight of oxygen (O) using the periodic table of elements; this value is 15.9994.
- 2
  Multiply the atomic weight of oxygen by the number of atoms to compute the mass of the O2 molecule. This mass is 15.9994 x 2 = 31.9988.
- 3
  Round the result of the mass calculation if necessary; for instance, oxygen mass rounding to thousandth yields 31.999. This is the mass in grams of one mole of oxygen gas.
Calculating Mass by Volume
- 4
  Find the density of oxygen gas -- that is 1.331 kg per cubic meter.
- 5
  Divide the density by 1,000 to convert it to kilograms per liter; 1.331 / 1,000 = 0.00133 kilogram/L.
- 6
  Multiply the volume by density to calculate the mass of the oxygen gas; for example, 40 liters of O2 weigh 40 x 0.00133 = 0.0532 kg or 53.2 g.

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