Question:
What is the chemical formula of rust?
What is the chemical formula of rust?
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Rusting requires both oxygen and moisture. Iron does not rust in completely dry air or in water without dissolved oxygen.
Updated On: Jun 9, 2026
- Hydrated ferrous oxide
- Only ferric oxide
- Hydrated ferric oxide
- None of these
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Verified By Collegedunia
The Correct Option is C
Solution and Explanation
Concept:
Rusting is a slow chemical process in which iron reacts with oxygen and moisture present in the atmosphere. This process is a type of corrosion that gradually destroys iron objects.
The simplified chemical reaction for rusting is:
\[
4Fe + 3O_2 + xH_2O \rightarrow 2Fe_2O_3\cdot xH_2O
\]
The reddish-brown substance formed is known as rust.
Step 1: Understand the composition of rust. Rust is not pure iron oxide. It contains water molecules trapped within the iron oxide structure. Therefore, rust is called a hydrated oxide.
Step 2: Identify the type of iron oxide. The iron present in rust is in the ferric state (\(Fe^{3+}\)). Hence the compound formed is ferric oxide: \[ Fe_2O_3 \] Since water molecules are attached, the complete formula becomes \[ Fe_2O_3\cdot xH_2O \] which is known as hydrated ferric oxide.
Step 3: Select the correct option. Therefore, rust is chemically represented as: \[ Fe_2O_3\cdot xH_2O \] and is called hydrated ferric oxide. Hydrated ferric oxide
Step 1: Understand the composition of rust. Rust is not pure iron oxide. It contains water molecules trapped within the iron oxide structure. Therefore, rust is called a hydrated oxide.
Step 2: Identify the type of iron oxide. The iron present in rust is in the ferric state (\(Fe^{3+}\)). Hence the compound formed is ferric oxide: \[ Fe_2O_3 \] Since water molecules are attached, the complete formula becomes \[ Fe_2O_3\cdot xH_2O \] which is known as hydrated ferric oxide.
Step 3: Select the correct option. Therefore, rust is chemically represented as: \[ Fe_2O_3\cdot xH_2O \] and is called hydrated ferric oxide. Hydrated ferric oxide
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