AQA GCSE FOUNDATION Chemistry: Corrosion and Its Prevention

AQA GCSE Foundation Chemistry: Corrosion and its Prevention

What is Corrosion?

Corrosion is the gradual destruction of materials by chemical reactions with their environment. The most common type of corrosion is rusting, which happens when iron or steel reacts with oxygen and water.

How Does Rusting Occur?

• Iron reacts with oxygen: In the presence of water, iron atoms lose electrons and form iron(III) ions (Fe³?).
• Oxygen gains electrons: Oxygen molecules gain electrons to form oxide ions (O²?).
• Rust forms: The iron(III) ions and oxide ions combine to form hydrated iron(III) oxide, commonly known as rust (Fe?O?.xH?O).

Methods to Prevent Rusting

There are several methods to prevent rusting:

1. Coating the Metal:

• Painting: A layer of paint acts as a barrier, preventing oxygen and water from reaching the metal surface.
• Oiling or Greasing: Oils and greases create a protective layer that repels water and oxygen.
• Electroplating: A thin layer of a more resistant metal (e.g., chromium or zinc) is deposited on the iron surface, acting as a barrier.

2. Sacrificial Protection:

• Galvanizing: A thin layer of zinc is applied to iron. Zinc is more reactive than iron and will corrode first, protecting the iron.
• Using a Sacrificial Anode: A more reactive metal (e.g., magnesium) is attached to the iron structure. The sacrificial anode corrodes first, preventing the iron from rusting.

3. Other Methods:

• Alloying: Adding other metals to iron can create alloys like stainless steel, which are more resistant to corrosion.
• Cathodic Protection: An electric current is applied to the iron structure, preventing the flow of electrons and thus inhibiting rust formation.

Examples of Rust Prevention in Everyday Life:

• Cars: Galvanized steel bodies, painted surfaces.
• Bridges: Sacrificial anodes, painted structures.
• Tools: Oiled or greased surfaces, protective coatings.
• Kitchen Sinks: Stainless steel (an alloy) is used.

Summary

Corrosion is a chemical process that damages metals. Understanding the process of rusting and the various methods of prevention is essential in everyday life. These methods help to extend the lifespan of metal objects and protect them from the damaging effects of corrosion.