Problem: How much oxygen in the air?
Objective: The student will find out how much oxygen there is in a milk bottle full of air.
Background: Air composed approximately of one-fifth oxygen and four-fifths nitrogen, with traces of a few other gases. Experiments with convection currents prove that a flame must have a constant supply of air if it is to remain alight.
Materials: Candle, empty milk bottle, dish of water.
Procedure: Fill dish with water, light a stub of candle and carefully float it in the dish. When the flame has established itself and is burning steadily, cover it with the upturned milk bottle.
What do you observe? Write in your journal your own observation.
Conclusion: The candle will continue to burn for a few seconds because it has a small supply of oxygen available in the air now trapped inside the bottle. The flame will use this oxygen quite quickly and then be extinguished. At the same time, because the oxygen content of the bottle has been used, an area of low pressure will result. The outer air, pressing down upon the surface of the water in the dish in its endeavor to enter, will instead, force water up into the bottle, thus indicating the amount of the oxygen which has been used.