# Rusting and corrosion

> What air and water do to iron, and how we stop it


## Objectives

- Describe rusting as the corrosion of iron by oxygen and moisture in air.
- Explain why rusting continues: rust is porous and flakes off.
- Explain how coatings (paint, oil, zinc in galvanizing, plating with another metal) protect iron.

## 1. Rusting and corrosion: from zero




## 2. Nail vs ring

An iron nail in a wet garden turns red-brown in weeks. A gold ring can last for centuries. What happens to the nail?


## 3. Corrosion

Corrosion The slow reaction of a metal with substances in the air, like oxygen and moisture, that wears the metal away. **Rusting** is the corrosion of iron. Rust is a hydrated iron (III) oxide. Some metals corrode quickly, like iron; gold hardly at all. Rusting is the corrosion of iron


## 4. Which nail rusts?

Predict: after a week, which nail rusts?

- A: dry air
- C: air and water ✓
- B: boiled water under oil

Nail C, in air and water, is the one that rusts. Rusting needs oxygen and moisture together: tube A has dry air, and in tube B boiling removed the air from the water and the oil keeps air out.

[ar-EG] المسمار C، اللي في هوا وماية، هو اللي بيصدّي. الـ rusting محتاج الـ oxygen والرطوبة مع بعض: الأنبوبة A فيها هوا ناشف، وفي الأنبوبة B الغليان طرد الهوا من الماية والزيت بيمنع الهوا يدخل.
## 5. How to stop rusting

Paint, oil, grease A barrier layer on bridges, car bodies and chains. Galvanizing Coating iron with a layer of zinc. Plating Covering iron with a thin layer of another metal that resists corrosion. Each coating keeps oxygen and moisture away from the iron.


## 6. Apply it

A bicycle chain is kept oiled. Why does it rust slowly?

- The oil keeps oxygen and moisture away from the iron ✓
- A moving chain is too fast to rust
- The oil reacts with the rust and removes it
- Oil makes iron a less active metal

The oil coats the chain and keeps oxygen and moisture away from the iron surface, so rusting is slow. The oil does not remove rust or change the iron itself.

[ar-EG] الزيت بيغطي الجنزير وبيبعد الـ oxygen والرطوبة عن سطح الـ iron، عشان كده الـ rusting بيبقى بطيء. الزيت مش بيشيل الـ rust ولا بيغيّر الـ iron نفسه.
## 7. Summary

Corrosion: a metal slowly reacts with oxygen and moisture in air. Rusting is the corrosion of iron. Rust is porous and flakes off, so rusting continues. Paint, oil, galvanizing (zinc) and plating with another metal keep air and moisture away. Key words: **oxygen and moisture**, **porous**, **galvanizing**, **resists corrosion**. Next in Chapter 1: chromium is a very active metal, yet it resists the air. Keep 'porous' in mind. Can you explain why a scratch in the paint lets a car door rust? At the scratch the paint is gone, so air and moisture reach the bare iron. Rusting needs oxygen and moisture together, so the iron rusts there.



Chapter: Transition Elements (https://yaani.ai/en/learn/chemistry/chem-s3-en.ch1)
Source: https://yaani.ai/en/lesson/chem-s3-en.lesson-chem.rusting-corrosion