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Corrosion of Copper · Green Patina

Class 10 · CBSE / CPC
All labs
NEO-LAB 7.0 | Rusting of Copper (Green Patina)
Class 10 · CBSE / CPC · Chemical Reactions & Corrosion
LIVE COPPER SIM
Cu + H2O + CO2 + O2
Green Patina (Verdigris)
Visual + Sound
Rusty Rust Copper Visualizer
Adjust atmosphere → Watch green patina grow on copper
Copper Strip (Cu) Atmospheric Corrosion Chamber
Moisture / Humidity
LOW
Air / Oxygen
LOW
CO₂ / Pollutants
NONE
Time Exposed
0 days
Patina Level 0%
Copper surface is shiny · No green patina yet. CLEAN COPPER
Control Console
2Cu + H2O + CO2 + O2 → Cu2(OH)2CO3
Word equation: Copper + Water + Carbon dioxide + Oxygen → Basic copper carbonate (green patina)
Moisture / Humidity LOW
CPC: Atmospheric corrosion of copper is faster in moist air.
Air / Oxygen LOW
Oxygen is required to convert copper into green patina.
CO₂ / Pollutants NONE
Basic copper carbonate forms in moist air containing CO₂.
Time Progress 0 days
Patina builds slowly over days, months and years.
Quick CPC Scenarios

What this experiment shows

Copper does not rust, but it does corrode. In damp air it first dulls to a brown-black oxide, and over years it develops the familiar green patina seen on old roofs and on the Statue of Liberty. The green layer is a mixture of basic copper carbonate and, near industry or the sea, basic copper sulfate or chloride. Unlike rust it clings tightly, so it protects the metal underneath instead of flaking away.

2Cu + H2O + CO2 + O2 → Cu2(OH)2CO3

What you need

  • Clean copper foil or sheet
  • A damp chamber, or a closed jar with wet paper
  • Dilute acid to clean the surface first
  • Time - the real process takes years

How it is done

  1. Clean the copper so you start from bare metal.
  2. Keep one piece in dry air and one in damp air containing carbon dioxide.
  3. Leave them side by side and record the colour at intervals.
  4. Compare with a piece kept in a sealed dry container.

What you should see

  • Bright copper dulls to brown, then to black oxide.
  • In damp air containing carbon dioxide, a green-blue layer slowly appears.
  • The patina sticks to the surface, so corrosion slows down rather than speeding up.
  • Dry air alone produces almost no change.

Where marks are lost

  • Calling the green layer "copper rust". Rust is an iron compound only.
  • Saying the patina is copper oxide. The green colour is a basic carbonate.
  • Missing the contrast with iron: rust flakes off, patina protects.
  • Ignoring the carbon dioxide. Damp air alone gives the oxide, not the green layer.

Questions students ask

Why is the Statue of Liberty green?
Its copper skin has reacted over more than a century with damp air, carbon dioxide and sulfur compounds to form a stable basic copper salt layer.
Is the patina a problem?
No. It is adherent and impermeable, so it seals the metal underneath. That is why copper roofs last for centuries.
Why does copper not rust?
Rust is specific to iron. Copper is below hydrogen in the reactivity series and corrodes far more slowly, by a different route and to different products.

Try these next

Written for Cambridge IGCSE Chemistry 0620 and CBSE Class 9-12 by Ajay Shekhawat, founder of MrChemCoach. Run the simulator above, then check yourself against the questions.