Specification Point 2.18:
Know the conditions in which Iron rusts
Conditions for Iron to Rust
Rust: A chemical reaction between Iron, Water and Oxygen to form Iron (III) Oxide. The corrosion of iron.
- Conditions: Oxygen and Water must be present for rust to occur
- Presence of sodium chloride increases speed of rusting
Iron + Water + Oxygen → Hydrated Iron (III) Oxide
4Fe (s) + 3O2 (g) + 2xH2O (l) → 2Fe2O3xH2O (s)
The requirements of Oxygen and Water for rust to occur
Specification Point 2.19:
Understand how the Rusting of Iron may be prevented by: Barrier Methods, Galvanising, Sacrificial protection
Prevention of Rust
- Barrier Methods:
- Rust can be prevented by coating iron with barriers that prevent the Iron from coming into contact with water and Oxygen.
- However, if the coatings are washed away or scratched, the Iron is once again exposed to water and Oxygen and will rust.
- Galvanising / Sacrificial Protection:
- Iron can be prevented from rusting using the reactivity series.
- Galvanising is when the iron is coated with a layer of zinc. ZnCO3 is formed when zinc reacts with oxygen in the air. This protects the iron by barrier method.
- If the coating is damaged or scratched, the iron is still protected from rusting by the sacrificial method (magnesium can also be used).
- This is because zinc is more reactive than iron so it reacts with oxygen and water and corrodes instead of the iron.
Example: Sacrificial Anode
Zinc Blocks Attached to the Hull of Ships so they will Corrode instead of the Hull
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Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.
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