An "empty" bottle is full of air: You can see and hear air flowing out of an ampoule, when you hold it under water in an upright position. When you discharge an ampoule with soap water, air bubbles into it replacing each portion of water leaving the ampoule.
This means that air is a substance with a certain mass. Assisted by an adult this can be measured using a 50-mL syringe and a digital pocket scale.
..
 
Material + 50.0 g weight
Syringe without air
Syringe with 50 mL air

A2 Air has a mass
Material (Fig. 1)
sterile disposable syringe (50 mL), transparent sticky tape, stop-cock for closing, digital pocket scale (70g/0,01g), weight (50.0g), nail (5 cm), flat pliers, candle, matches, beaker with water.
Preparation of the syringe
1. Protect the marking of the syringe by covering it with transparent sticky tape.
2. Tightly screw an open stop-cock into the syringe. Fill it with 50 mL of air.
3. Heat a nail above the flame of a candle. Press it through the piston to fix it at the 50-mL mark.
4. Remove the nail. Press the air out of the syringe.
Experiment
5. Close the stop-cock. Pull the piston to the 50-mLmark.
6. Fix it in this position pressing the nail through the hole in the piston..
7. Weigh the "empty" syringe on a digital pocket scale (Fig. 2). Write down the mass.
8. Take the syringe from the scale. Open the stop cock. Re-weigh (Fig. 3).
Observations
When the stop cock is opened, you can hear a fizzling.
In this experiment the mass of the syringe without air was 33.93 g (Fig. 2), with air it was 33.97 g (Fig. 3). This is an increase of 0.040 g = 40 mg.

back.............. ......,,....first publication: 22.01.2009.. ..................... last modification: 07.01.2011