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SAI INTERNATIONAL SCHOOL
CLASS-VII
SUBJECT- CHEMISTRY
TOPIC-PHYSICAL AND CHEMICAL CHANGES
SUB TOPIC- SOME COMMON CHEMICAL CHANGES

LESSON NOTE

Some Common Chemical Changes

Rusting of iron

Iron objects react with oxygen and moisture present in air to produce flaky redfish
brown colour substance is commonly known as rust.

Rusting is a chemical change where iron forms rust with the action of oxygen and
water. Rust or hydrated iron oxide is a new substance with different properties and it
cannot be back to iron again.

The process of rusting is represented as

Iron + Oxygen + Water Rust(hydrated iron oxide)

Fe O2 H2 O Fe2O3. xH2 O

Rusting of iron is a slow process and it destroys the whole iron object.

Iron is an important metal and is used in making bridges, cars, ships, trucks, building
materials etc. Rusting causes a lot of damages of iron articles.

Rusting of iron becomes faster if the content of moisture increases. We need to
prevent rusting to protect iron objects.

Methods of prevention of rusting:

1. Applying grease or oil on the exposed part of the iron articles.
2. Painting the surface of iron article.
3. Galvanising the surface of iron article (Galvanisation is a process in which a
layer of zinc is deposited on surface of iron electrolytically i.e by passing
electric current.
4. Electroplating the surface of iron with metal which are not attacked by
atmospheric moisture. The shining parts of the bicycles are given a coating of
chromium to protect from rusting.
5. Alloying

Rusting of iron requires both oxygen and water. Let us perform an activity to prove
this.

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