Corrosion Control
Iron rusts, but only under the right conditions - and there are clever ways to stop it. Learn what corrosion is, how to prevent rust, and why mixing metals into alloys makes them stronger.
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Why metals rust 🔩
**Corrosion** is what happens when a metal reacts with its surroundings and is slowly eaten away. For iron and steel, that corrosion is called **rust** - and it costs the world a fortune every year. The good news: rusting only happens under certain conditions, so we can **prevent** it. This module covers what corrosion is, how to stop rust, and why mixing metals into **alloys** makes them stronger.
The words you need 🧪
Four terms unlock the topic.
Match each term to its meaning 🔗
- Corrosion
- Sacrificial protection
- Electroplating
- Alloy
- The oxidation of a metal by reaction with oxygen
- Attaching a more reactive metal that corrodes instead
- Coating a metal with a thin layer of another by electrolysis
- A mixture of a metal with other elements
What rust needs 💧
What two substances must both be present for iron to rust?
- Both oxygen and water
- Only oxygen
- Only water
- Oxygen and carbon dioxide
How to stop rust 🛡️
Because rust needs oxygen AND water, we prevent it by keeping one or both away, or by a clever trick: - **Barrier methods** - paint, oil, grease or plastic keep out oxygen and water.\n- **Sacrificial protection** - attach a **more reactive** metal (zinc or magnesium); it corrodes instead of the iron. - **Galvanising** - coating iron with zinc does both: a barrier AND sacrificial protection.\n- **Electroplating** - a thin metal layer for appearance and corrosion resistance.
Preventing rust ✅
Select the TWO methods that would help prevent iron from rusting.
- Painting the iron
- Galvanising it with zinc
- Leaving it in salty water
- Keeping it permanently wet
Two ways to protect ⚖️
Barrier methods and sacrificial protection both stop rust, but they work differently - and one keeps working even when scratched.
Match each metal to its use 🏭
- Aluminium
- Copper
- Gold
- Brass
- Low density, used for aircraft bodies
- A good conductor, used for electrical wiring
- Unreactive, used for jewellery and electrical contacts
- A hard alloy, used for instruments and fittings
Why sacrifice a metal? 🔬
Why does sacrificial protection stop the iron from rusting?
- A more reactive metal is oxidised in preference to the iron
- It makes the iron heavier so water runs off
- It simply paints over the surface of the iron
- It removes all the water from the air
Corrosion in a paragraph ✏️
Corrosion is the _____ of a metal. Iron rusts only when both _____ and _____ are present. Coating iron with zinc gives _____ protection, because zinc is more _____ than iron.
Why alloys are stronger 🪜
An interactive activity.
Choose the protection 🧭
An interactive activity.
Your turn: explain ✍️
An interactive activity.
The grade-9 habit 🌟
The marks here hinge on precision. Rust is the **oxidation** of iron and needs **both oxygen and water** - stating just one loses the point. Prevention works by removing a condition (**barrier** methods) or by **sacrificial protection**, where a **more reactive** metal is oxidised in preference. And for alloys, always give the **particle reason**: different-sized atoms disrupt the regular layers so they cannot slide, making the alloy harder and stronger than the pure metal.