Does Air Have Mass?

You bet it does, and this demonstration proves it.

Equipment

  • balance
  • bicycle pump with pressure gauge
  • 2 L soda bottle
  • soda bottle cap fitted with a bicycle tire valve

Presentation

  1. The 2 L bottle is capped at atmospheric pressure and placed on a tared balance to get its initial mass
  2. The bottle is removed from the balance, connected to the air pump, and pressurized to about 20 psi.
  3. Bottle and air mass are measured again to show that it is about 3 grams heavier.

Details

This demo is a very clean way to show that air has mass since the only variable that is changed is the number of moles of gas inside the container.  A reasonably small pressure (20 psi) is sufficient to show a measureable change in mass.  The pressure of the bottle should be kept below 60 psi to avoid it rupturing and exploding.  This demo is also an excellent demonstration of Avogadros Law since it would show that the pressure and mass scale linearly for a fixed volume.

Safety

explosion

Special Safety Notes

  • The pressure inside the bottle should be kept below 60 psi to avoid explosion.  
  • Inspect the bottle for damage prior to pressurizing it.
airmass
All of the equipment used in this demo.
airmass2
A different view of the equipment.