Grade 10 · 🧪 Chemistry · Chemical reactions
What makes iron rust?
Set up four nails in different conditions and find out which ingredients rusting really needs.
Why this matters
Rusted corrugated iron roofs, bridges and water pipes cost Ethiopia millions of birr to replace every year. Engineers protect metal by painting, oiling or galvanizing it. In this experiment you'll discover exactly what causes rust, so you can understand how those protections work.
Watch the demo
Video coming soon
We're recording a demo for this experiment. Until then, follow the step-by-step guide below.
The science
Rusting is oxidation
Rust is hydrated iron oxide. It forms when iron reacts with oxygen and water: 4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O. Salt speeds it up because it makes water a better conductor.
A fair test
To find which factor matters, change only one condition at a time and keep everything else the same. That way, any difference must be caused by that condition.
You'll need
- 4 identical iron nails (not galvanized — shiny, not dull grey)
- 4 clear cups or jars
- Water, salt and cooking oil
- Boiled, cooled water↳ Boiling removes most dissolved air
- Labels or a marker
Safety first
- Ask an adult to help boil the water.
- Wash your hands after handling rusty nails.
Step by step
0/6 doneWhat you should see
Nail D (salt water) rusts fastest, followed by B (tap water). Nail A (dry) and nail C (no air) show little or no rust.
Why it happens
Rusting needs both oxygen and water. Cup A has no water and cup C has almost no oxygen, so neither rusts much. Salt dissolves into ions that help electrons move during the reaction, which speeds up rusting — that's why metal rusts faster near salty roads or the sea.
Didn't work? Try this
None of the nails rusted.
Your nails are probably galvanized or stainless. Use plain iron nails, or scrub them with sandpaper first.
Nail C rusted too.
Some air got in. Make sure the oil layer completely covers the water and the nail is fully submerged.
Still stuck? Ask the lab assistant
Check your understanding
1. Which two things are both needed for iron to rust?
2. Why does painting a roof stop it rusting?
Your lab notebook
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