To show that oxygen is necessary for the combustion of a substance.
Combustion is the name given to the chemical reaction in which a substance reacts with oxygen to produce heat. The substances which undergo combustion are called combustible substances or fuel. Fuel can be solid, liquid, or gaseous.
There are various types of combustions such as rapid combustion, spontaneous combustion, explosion, etc. In rapid combustion, the gas burns rapidly and generates heat and light. The spontaneous combustion is a type of combustion where a substance spontaneously catches fire without any externally applied trigger. On the other hand, an explosion is a sudden reaction that involves the generation of heat, light, and sound. Such reaction results in the release of a large amount of gas.
Air is necessary for combustion. During the process of combustion, the fuel burns in oxygen (present in air) to produce carbon dioxide, water and energy in the form of heat and light. Combustion cannot happen without oxygen. Approximately 21% of the air in Earth's atmosphere is oxygen. This oxygen is utilized in burning. In fact, the three components that are needed to sustain a fire —oxygen, heat, and fuel—are collectively known as the fire triangle. Removing any of these three elements extinguishes the fire.
Eliminating the fuel source for example turning off gas valve can easily stop combustion. Another method is to add water to the fire, which reduces heat because most of the heat is used to turn the water into steam. Cutting off the oxygen supply is another approach that can be used to stop fire. Most fire extinguishers work by separating the fuel from the oxygen. Since the oxygen must come into contact with the fuel, if the fuel is covered with something that keeps the oxygen away, the fire will go out. This is the rationale behind why we cover someone with a blanket to put out a fire when his or her clothing catches on fire.
If you perform an activity that involves covering a candle with a beaker, the candle within the beaker will continue to burn until the air inside the beaker is completely depleted of oxygen. After that, the lack of oxygen causes it to stop burning. This experiment demonstrates that oxygen is essential for burning.
Some examples of combustion are: