Page 30 - Curriculum Visions Dynamic Book

Corrosion
One of the most important properties of most oxides is that they are insoluble. Thus when a highly reactive metal, such as aluminium, is exposed to the air, it very quickly reacts with the oxygen in the air and develops a thin oxide coating.
The oxide coating is almost invisible and it is gas and watertight. This is what prevents further reaction with air (corrosion). It also explains why there is an apparent contradiction between the reactivity of a metal like aluminium, and its apparent immunity from corrosion.
One of the important consequences of such rapid oxidation is that many goods can be manufactured from a wide variety of metals without risk of them disintegrating quickly. Objects from toys to vehicles, houses to skyscrapers rely on metals developing a protective oxide coating.
Unfortunately, one of the most widely used metals, iron, does not develop a watertight oxide coating. This is the reason iron corrodes,
a process known as rusting. As a result, while aluminium can be used for external cladding without treating it, steel must be covered with a coating (for example paint) to protect it from the effects of water.
 An iron nail placed in a jar of water quickly rusts.
EQUATION: The rusting of iron
Iron + water + oxygen ➪ ferric oxide + water 4Fe(s) + 6H2O(l) + 3O2(g) ➪ 2Fe2O3(s) + 6H2O(l)
Rust
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