Combustion is the process that takes place when oxygen atoms, heat and a fuel source react with each other. Combustion is also called burning. Do not try combustion experiments without having a fire extinguisher ready and a series of safety precautions that kids fully understand prior to starting the experiments.
Most children think that a fire burns yellow. This is because the students have observed wood burning. Most woods contain sodium, which produces a yellow flame. Explain to kids that different chemicals present within the fire may change the colour of the flame. Use chemicals that can change the colour of the flame in an experiment. For example, borax, which can be purchased at grocery stores, will burn a light green colour. Potassium chloride, which is water softener salt, will produce a purple colour. This activity should be completed outside or in a well-ventilated area.
Children will be amazed that a dollar bill can be set on fire without burning the bill itself. Combine water and alcohol to create a mixture in which to dip the bill. The proper ratio of water to alcohol differs based on what type and concentration of alcohol you use (test it on ordinary paper before lighting currency). Dip the bill into the liquid with tongs and squeeze out the excess. Holding the bill with the tongs, light the bill at the bottom. The alcohol burns at a lower temperature than the fabric of the dollar. The water helps keep the temperature from reaching the combustion threshold of the bill by boiling and evaporating off as the bill burns. If this is conducted correctly, you will be left with a damp bill.
Invisible Fire Extinguisher
Combustion reactions require three things: oxygen, heat and fuel, which creates what is known as the fire triangle. Cut off the top of a two-liter bottle and combine vinegar and baking soda in the bottom. Let the mixture bubble until the reaction is complete. Light a candle and lower it into the bottle. The candle will go out immediately once it is lowered into the bottle. The reaction of vinegar and baking soda has created large amounts of carbon dioxide, removing all the oxygen from the area and extinguishing the candle.
Mesh Screen Fire Extinguisher
If any of the three items required for combustion is removed, the fire will go out. In the invisible fire extinguisher experiment, the oxygen is removed. Kids may wonder how heat can be removed. One way is to throw water on the fire. Water removes the heat through boiling and steam. But there are other ways. Light a candle and show it to the class. Take a fine wire mesh screen and place it over the top of the candle. The flame will go out. The mesh distributes the heat over the screen, removing heat from the flame and causing it to go out.