Reactivity and Corrosion: Iron and Aluminium

Reactivity with Air

Iron and aluminium react differently with air due to their distinct properties:

• Iron (Fe): When exposed to air, iron reacts with oxygen to form iron(III) oxide, commonly known as rust. This process is slow and requires moisture.
• Aluminium (Al): Aluminium reacts with oxygen to form a thin, protective layer of aluminium oxide on its surface. This layer prevents further oxidation.

Reactivity with Water

The interaction of iron and aluminium with water varies:

• Iron: Iron reacts with water and oxygen to form rust, especially in the presence of saltwater, which accelerates the process.
• Aluminium: Aluminium does not react with water due to its protective oxide layer.

Reactivity with Acids

Both metals react with acids, but in different ways:

• Iron: Reacts with dilute acids like hydrochloric acid (HCl) to produce iron salts and hydrogen gas. For example, $\text{Fe} + 2\text{HCl} \rightarrow \text{FeCl}_2 + \text{H}_2$.
• Aluminium: Reacts vigorously with acids, producing aluminium salts and hydrogen gas. For example, $2\text{Al} + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2$.

Rust Prevention

Preventing rust involves stopping the reaction of iron with oxygen and moisture:

• Painting and Coating: Applying paint or a protective coating prevents exposure to air and moisture.
• Galvanization: Coating iron with a layer of zinc protects it, as zinc reacts preferentially with oxygen.
• Alloying: Mixing iron with other metals (e.g., chromium in stainless steel) enhances resistance to rust.