1. What has happened here and why?

2. What is corrosion?
Corrosion is a gradual chemical reaction which involves the surface of a metal changing from an element to a compound.
Over time, corrosion changes the appearance of the metal as it breaks down and it becomes weaker.
Corrosion can seriously damage metallic objects and structures.
Coating the surface of a metal with paint and certain chemicals can protect it from corrosion.
Photo credit: Piotr Sss
Corroded metal door handle.
What happens if the protective coating becomes damaged?

3. Do all metals corrode?
Metals behave differently when exposed to the environment.
Gold is an unreactive metal and does not corrode easily.
In many cultures, gold is considered a precious metal and is used to make sacred and decorative objects.
Items made from gold can survive for thousands of years and have even been found in good condition underwater.
Photo credit: © 2007 Jupiterimages Corporation.
In general, objects made from metals that corrode easily do not survive for as long.

4. What happens to iron when it rusts?
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Rusting is the specific name given to the corrosion of iron.
It is a chemical reaction between iron, oxygen and water.
Rusting is an oxidation reaction which leads to the formation of hydrated iron (III) oxide - the chemical name for rust.
Photo credit: Jill Smith
Teacher notes
Ferroxyl indicator solution turns blue in the presence of Fe2+ ions, and so can be used to detect the chemical change that can lead to rust.
water
oxygen
hydrated iron (III) oxide (rust)
iron + →
4Fe (s)
2H2O (g)
2Fe2O3.H2O
3O2 (g)

5. Rate of corrosion experiment

6. It’s actually the oxygen in air
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In order for iron to rust
Oxygen and water’s a must,
Air alone won’t do
Without water there too,
So protect it, or get a brown crust!
It’s actually the oxygen in air

7. Protecting from rust

8. Sacrificial protection

9. Sacrificial protection
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Sacrificial protection
Zinc is electrically connected to the iron. Any water or oxygen reacts with the zinc (or magnesium) instead of the iron.
Coating in zinc is called galvanization and it works even when the zinc coating is scratched.

10. How do we treat our drinking water?
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Drinking water is made fit for domestic home consumption by
(i) allowing sedimentation to occur, where larger insoluble particles settle out
(ii) passing it through sand filter beds to remove finer solid particles
(iii) treating with chlorine to kill bacteria
(iv) adding small amounts of sulphur dioxide to remove excess toxic chlorine