Is oxygen gas heavy than air?

Answer 1

On average, oxygen (O2 which is 2 oxygen atoms) makes up about 20-21% of air. The bulk of the rest of it is Nitrogen (N2 which is 2 nitrogen atoms) (about 78%).

Oxygen has a molecular weight of about 16 per atom. Nitrogen has a molecular weight of about 14 per atom. Pure Oxygen gas is thus heavier than "air."

For example:

Say you had a sample of air containing 8 Nitrogen atoms and 2 Oxygen atoms (80% N2, 20% O2). Based on atomic weight, it would come in at 150. (150 is calculated by multiplying the 8 nitrogen atoms by = 112, and then multiplying the 2 oxygen atoms by 16 = 32, and adding 112 and 32 together = 150).

If you had the same amount of pure oxygen gas (O2), you would have 10 oxygen atoms times 16 = 160.

So as a rough approximation, if the weights of oxygen gas = 160 and air = 150, air is approximately 93.75% the weigh of oxygen gas.. or in other words, "air" is approximately 6.25% lighter than pure oxygen gas.

Answer 2

Oxygen gas has a slightly higher molecular weight compared to the average molecular weight of air, so in that sense, it can be considered heavier than air. However, oxygen makes up only about 21% of the air we breathe, so the overall weight of oxygen in the air is not enough to significantly affect its overall density or make it noticeably heavier than air.