One very simple experiment can demonstrate the most basic principle of combustion: it requires oxygen. To illustrate this, students light candles inside jars. As long as the jars are open, the flames will continue to burn. Cover the lid and the flame will flicker and quickly go out. This experiment can be repeated with jars of different sizes. Students will note that the candles in the larger jars, which held more oxygen than the smaller ones prior to being covered with the lid, will burn for a little bit longer before going out. Putting the lid on the candle does not extinguish the flame. The exhaustion of the supply of oxygen is what does it.
Add a few milliliters of hydrogen peroxide to a ½ teaspoon of yeast in a test tube. A detailed analysis of this reaction can be the subject of an entirely different lesson, but for now students should take it on faith that it does produce oxygen. Immediately ignite a small splint of wood and blow it out carefully after a few seconds so that the end is still glowing and hot. If you place this into the test tube, it should reignite. This is another illustration of the role of oxygen in combustion.
Ignite your trusty laboratory Bunsen burner, following all proper safety techniques. Adjust the collar at the base of the burner to allow maximum flow of air into the device. The flame is blue. If you have a laboratory thermometer, take note that the flame is about 700 degrees Celsius. Adjust the collar to restrict air flow. The flame will change from blue to yellow. The temperature will drop to about 300 degrees. The hot blue flame is produced when there is adequate oxygen for the methane to undergo complete combustion. The cooler yellow flame is a product of incomplete combustion.
Adjust the Bunsen burner collar to produce the "cool" yellow flame. Using tongs, suspend a porcelain dish just above this flame. After a few seconds, you may notice a black spot on the dish. Try the same thing with the dish above the hot blue flame. There should be little or no accumulation of black soot. The blue flame is undergoing complete combustion. Every carbon atom in the fuel supply finds two oxygen atoms to combine with to form CO2. But when oxygen is limited, some carbon accumulates on the dish rather than being completely converted to CO2.