I think Air is not weightless. Every mole or 24 dm3 of air will consist of about Nitrogen-78.1%
Oxygen- 20.9%
and 1% other gases (with Carbon Dioxide- 0.035%)..
Assuming 79% of Nitrogen and 21% of oxygen are present, then each mole of air will weigh 0.79*14 + and 0.21*16= 14.42 g.
Its...