Metals slowly spoil
Green on copper, black on silver, brown on iron.
The dull coin
A copper pot left in the open turns dull and greenish. Old silver turns black. Iron turns brown. Why do metals lose their shine?
A shiny copper coin and a shiny silver ring are left in the open air for a very long time. What will happen to them?
What this lesson covers
The idea
Corrosion is the gradual deterioration of metal surfaces caused by air, water or other substances, seen as rust on iron, a green coating on copper and a black coating on silver.
The dull coin
A copper pot left in the open turns dull and greenish. Old silver turns black. Iron turns brown. Why do metals lose their shine?
A shiny copper coin and a shiny silver ring are left in the open air for a very long time. What will happen to them?
- They stay as shiny as new
- Each gets a coating of a different colour
- They both get brown rust like iron
Iron, copper and silver in the open
Slide the time forward until the objects have changed. Then tap each object to name its coating.
Corrosion
The gradual deterioration of metal surfaces caused by air, water or other substances is called corrosion. Rusting of iron is one kind of corrosion.
Rusting is a serious problem in our country. Every year, an enormous amount of money is spent to replace or repair iron structures damaged by rusting.
The Iron Pillar of Delhi was made in the time of Chandragupta II, more than 1600 years ago. It is about 8 metres high and weighs more than 6000 kilograms. After all these years of wind and rain it has barely any rust. It was made in a way that resists rusting, which shows the skill of ancient Indian metal workers.
- Metal | What forms on its surface
- Iron | brown deposit (rust)
- Copper | green coating
- Silver | black coating
Notes
Corrosion is the gradual deterioration of metal surfaces caused by air, water or other substances: brown rust on iron, a green coating on copper and a black coating on silver.
Check yourself
The gradual deterioration of metal surfaces caused by air, water or other substances is called...
A green coating forms on the surface of an old...
Which pair is matched correctly?
Which of these is a kind of corrosion?
- corrosion — correct. Yes! Rusting is one example of it.
- conduction. Conduction is the transfer of heat along a material.
- ductility. Ductility is being drawn into wires.
- silver ring. Silver gets a black coating.
- copper object — correct. Yes! Copper gets a green coating.
- iron nail. Iron gets a brown deposit.
- Silver, black coating — correct. Yes! Silver gets a black coating.
- Copper, black coating. Copper gets a green coating.
- Iron, green coating. Iron gets a brown deposit called rust.
- Gold being beaten into a thin sheet. That is malleability, not corrosion.
- A copper wire carrying current. Carrying current does not spoil the surface.
- Rust forming on an iron nail — correct. Yes! Rusting is corrosion of iron.