# Molecular weight of air

How to calculate molecular weight of air

 Unknown008 Posts: 8,147, Reputation: 3745 Uber Member #2 Jan 16, 2010, 12:35 AM

Well, all you can do is approximate it.

What is the composition of air?
Nitrogen gas 78%
Oxygen 21%

An approximate molecular weight would be the average of those two gases which are the most abundant.

78% is of mass 28 g
21% is of mass 32 g.

100% would have approximately $\frac{(78% \times 28) + (21% \times 32)}{78% + 21%} \times 100% \approx 28.8$

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