The rusting of iron is a common example of a corrosion process that occurs when iron is exposed to oxygen and moisture. It is an electrochemical reaction that involves the oxidation of iron and the reduction of oxygen.

The mechanism of rusting can be explained in the following steps:

1. Formation of Iron(II) Ions: In the presence of moisture (water or humidity), iron reacts with oxygen from the air to form hydrated iron(II) ions, also known as ferrous ions (Fe²⁺):2 Fe(s) + 2 H₂O(l) + O₂(g) → 2 Fe²⁺(aq) + 4 OH⁻(aq)This reaction occurs on the surface of the iron.
2. Formation of Iron(III) Hydroxide: The ferrous ions react further with hydroxide ions (OH⁻) in the presence of oxygen and water to form iron(III) hydroxide, which is a greenish precipitate:4 Fe²⁺(aq) + O₂(g) + 4 H₂O(l) → 4 Fe(OH)₃(s)This step occurs in areas where moisture is present.
3. Conversion to Rust: Iron(III) hydroxide is not stable and undergoes dehydration and oxidation processes to form hydrated iron(III) oxide, commonly known as rust:2 Fe(OH)₃(s) → Fe₂O₃·xH₂O(s) + 3 H₂O(l)The rust appears as a reddish-brown or orange coating on the surface of the iron.
4. Continuation of Reaction: The presence of moisture and oxygen sustains the rusting process, allowing it to progress further and spread across the iron surface. This ongoing electrochemical reaction involves the continuous oxidation of iron and reduction of oxygen.

The rusting process can be accelerated by factors such as exposure to saltwater, acidic conditions, and high humidity, which increase the rate of corrosion.

It’s important to note that the rusting of iron is an undesirable process that leads to the deterioration of iron objects and structures. To prevent rusting, protective measures such as coating with paint, applying anti-corrosion coatings, or using sacrificial anodes (such as zinc or magnesium) can be employed to inhibit the contact of iron with oxygen and moisture.