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What is the chemical formula of rust which is f... - JAMB Chemistry 2023 Question

 

What is the chemical formula of rust, which is formed on the surface of iron in the presence of oxygen and moisture?

A

Fe\(_3\)O\(_4\)

B

FeO

C

Fe(OH)3

D

Fe\(_2\)O\(_3\)

correct option: d

Rust is a common name for a very common compound, iron oxide. Specifically, rust refers to the reddish-brown substance that forms on the surface of iron or steel when it reacts with oxygen and moisture in the presence of air. The chemical process through which this corrosion occurs is known as oxidation.

The primary chemical formula for rust is **Fe₂O₃**, but the exact composition can vary. Rust is often a mixture of iron oxides and hydroxides, and it's commonly represented as a hydrated iron(III) oxide, denoted as \(Fe_2O_3 \cdot nH_2O\), indicating the presence of water molecules.

The formation of rust can be represented by the following simplified chemical equation:

\[ 4Fe + 3O_2 + 6H_2O \rightarrow 4Fe(OH)_3 \]

This process is accelerated by the presence of electrolytes (such as salts) and is commonly observed on objects made of iron or steel exposed to the atmosphere, especially in humid conditions. Rusting is a significant concern as it can weaken structures and objects made of iron or steel over time.

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