Corrosion and Rusting
Iron rusts when it meets oxygen and water.
About this topic
Corrosion is the gradual destruction of a metal by chemical reaction with its environment. Rusting is the corrosion of iron, needing both oxygen and water: 4Fe + 3O2 + 2xH2O → 2Fe2O3·xH2O. Rust is flaky and falls away, exposing fresh metal, so rusting continues. Salt and acid speed it up.
Rusting is an electrochemical process. In one area of an iron surface, iron is oxidised (Fe gives Fe2+ + 2e-), forming the anode; electrons travel through the metal to another area where oxygen is reduced to hydroxide, the cathode; then Fe2+ reacts further to form hydrated iron(III) oxide. Salt water provides ions that carry current, which is why cars rust faster near the sea or on salted roads.
Prevention methods include painting, oiling or plastic coating to keep out air and water; galvanising, coating steel with zinc, which also protects sacrificially because zinc is more reactive and corrodes first; sacrificial anodes of magnesium bolted onto ship hulls and pipelines; making stainless steel by alloying with chromium, which forms a thin protective oxide layer; and electroplating. Aluminium resists corrosion because its oxide layer sticks tightly.
A misconception is that rust protects like aluminium oxide does; iron rust is porous. Another is that corrosion only happens to iron; silver tarnishes and copper turns green.
Key ideas
- Galvanising protects
- Sacrificial anodes
- Rust is Fe₂O₃·nH₂O
Quick check
Use cases: where Corrosion and Rusting helps
- Homework: review the key idea behind Corrosion and Rusting before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Corrosion and Rusting without notes.
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Frequently asked questions
What is Corrosion and Rusting?
Iron rusts when it meets oxygen and water.
What will I learn in Corrosion and Rusting?
Galvanising protects. Sacrificial anodes. Rust is Fe₂O₃·nH₂O.
Is Corrosion and Rusting part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Corrosion and Rusting lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Corrosion and Rusting?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
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