What Is Rust

Rust is formed when iron reacts with oxygen in the air. The product is iron oxide, which is commonly known as rust.

Iron+ oxygen=iron oxide

This means that the iron changes and no longer has the same properties. A strong iron girder can become rusted and fall apart. This could mean that a building collapses.

Rust is only formed when both oxygen and water are present. Water is not part of the equation above but it is needed for the reaction to happen.

What causes iron to rust?

A new iron nail is placed in each of four test tubes, as in the diagram above.

Test tube 1 contains nothing apart from the nail, and is open to the air.

Test tube 2 contains water and the nail is half in the water. The tube is open to the air. So this tube has water and the air.

Test tube 3 has calcium chloride in the bottom. The calcium chloride absorbs water into so the air inside the tube is dry. There is no water in this tube. The tube is stoppered.

Test tube 4 has water that has been boiled to remove as much dissolved gas as possible. On the top of the water is a layer of oil. This stops any air entering the water. The tube is stoppered. 

How can we protect iron?

There are ways that the iron can be protected so it does not rust.

• The iron can be painted. This stops the oxygen in the air reaching the iron.

• The iron can be galvanized. This means covering the iron with a layer of zinc. This again prevents the oxygen reaching the iron.