Oxygen is a part of the air that surrounds us. It can cause changes on different materials.
Some fruits, root crops and vegetables have enzymes which when combined with water gives it a
brown color, a sign of food spoilage. When these fruits are cut, oxygen is introduced into their cells
and enzymes rapidly oxidize their tissue and turn it into brown.
Another effect of oxygen is rusting. It is caused by the reaction of iron with oxygen present
in the air. The amount of rust formed in an iron depends on the moisture and humidity of the
surrounding.
Combustion also is among the common effects of the presence of oxygen. Three things are
needed for fire to occur, heat, fuel, and oxygen. A fire occurs when the three elements are present
in the right amount. The fire will continue its flame if there is a continuous supply of these three
elements.
In a burning candle, it requires oxygen to continue burning. If it is covered with a glass jar, it will
eventually go out on its own. The amount of time it takes for the lit candle to go out varies based
on the size of the jar. When the jar is placed over the top of the candle, there is still oxygen for the
fire to consume, but it is in a limited quantity. Once all the oxygen in the jar is exhausted by the
flame, it no longer has its fuel and goes out.
Materials will undergo physical change under the condition of lack of oxygen. The change affects
only the appearance of the matter and no new material is formed.

A. Direction: Match the original material with its product after the chemical change. Write the
letter of the correct answer on the space provided before each number.
_____ 1. burned paper a. spoiled milk
_____ 2. fermentation of coconut sap b. vinegar
_____ 3. leftover milk c. rust
_____ 4. undigested food d. ash
_____ 5. iron nail e. feces
B. Direction: Put / on the space provided if the materials undergo change with the presence of
oxygen and X if it undergoes a change due to lack of oxygen.
_____1. diced onion _____6. spoiled food
_____2. burnt paper _____7. pounding of chalk
_____3. souring of milk _____ 8. ironing of clothes
_____4. grinding coffee _____9. digesting of food
_____5. rusted iron _____10. tearing of paper