Review
Question: What is the name of substance which does get deposited over iron because of moisture present in air?
Correct Answer
Rust
ExplanationA substance called 'Rust' deposited over iron, when iron is exposed to moisture present in air for long time. Rust is reddish brown in colour. The chemical name of Rust is iron (III) oxide [Fe2O3. nH2O]. Formation of Rust corrodes the iron slowly and if not prevented, finally substances made of iron get destroyed completely over the time. Rusting is the oxidation of iron and its alloys. Or it can be said that Rusting is the corrosion of iron and its alloys.
When articles made of iron or its alloys, such as steel exposed to moisture present in air for long time, iron reacts with oxygen in presence of water present in air and get oxidised. And it turns into iron (III) oxide (Fe2 O3). The iron oxide deposited over the articles made of iron which is reddish brown in colour. In general term this iron (III) oxide is called Rust. Rust is actually hydrated iron (III) oxide [Fe2O3.nH2O].
This phenomenon is known as rusting of iron. It is also called corrosion of iron.
Rusting of iron is completed in two steps.
(a) First on reaction of iron with water and oxygen, iron (III) hydroxide [Fe(OH)3 is formed.
4Fe + 6 H2O + 3O2 → 4Fe(OH)3
Iron (III) hydroxide is known as ferric hydroxide also.
(b) In the long run ferric hydroxide gets dehydrated, and turns into iron (III) oxide [Fe2O3]. Iron (III) oxide is known as ferric oxide also.
4Fe(OH)3 → Fe2O3.nH2O
This Ferric oxide or Iron (III) oxide is known as Rust.
Rusting gradually starts eating up articles made of iron if not prevented and finally destroys them.