Discuss the redox reaction taking place in the rusting of iron in detail.

The rusting of iron is a type of oxidation-reduction (redox) reaction that occurs when iron reacts with oxygen and water in the environment. This process leads to the formation of iron oxides, commonly known as rust. Rusting is a complex electrochemical process that can be broken down into two main half-reactions: oxidation at the anode and reduction at the cathode.

Step-by-Step Process of Rusting:

  1. Oxidation at the Anode (Iron loses electrons): At the anode (where oxidation occurs), iron (Fe) is oxidized to form iron ions (Fe²⁺) by losing electrons:

    Fe(s)→Fe2+(aq)+2e−

    The iron atoms lose electrons to become iron ions. These Fe²⁺ ions dissolve into the surrounding water.

  2. Reduction at the Cathode (Oxygen gains electrons): At the cathode (where reduction occurs), oxygen molecules (O₂) from the air dissolve in water and undergo reduction by gaining electrons to form hydroxide ions (OH⁻):

    O2(g)+2H2O(l)+4e−→4OH−(aq)

    This reaction typically occurs in the presence of water (moisture), which facilitates the movement of electrons.

  3. Formation of Rust: The Fe²⁺ ions formed at the anode react with oxygen and water to form hydrated iron(III) oxide (rust):

    4Fe2+(aq)+O2(g)+4H2O(l)→2Fe2O3⋅3H2O(s)

    This is commonly known as rust (iron(III) oxide hydrate), a reddish-brown compound.

The overall reaction for rusting can thus be summarized as:

4Fe(s)+3O2(g)+6H2O(l)→4Fe(OH)3(s)

The iron(III) hydroxide (Fe(OH)₃) can further dehydrate to form iron(III) oxide (Fe₂O₃), commonly known as rust.

Key Points:

  • Oxidation: Iron loses electrons to form Fe²⁺ ions.

  • Reduction: Oxygen gains electrons to form OH⁻ ions.

  • Rust Formation: The combination of Fe²⁺ ions, oxygen, and water leads to the formation of iron oxide.

Factors Accelerating Rusting:

  • Presence of Water: Water is essential for rusting because it acts as a medium for the movement of ions.

  • Oxygen: The availability of oxygen in the atmosphere accelerates rusting.

  • Salt: Saltwater speeds up rusting due to its ability to conduct electricity, facilitating the electrochemical reactions.

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  14. Define oxidation in terms of electrons. Give an example.
  15. Define reduction in terms of loss or gain of oxygen or hydrogen. Give an example.
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