Question

even though statue of Liberty is made of copper it is green in colour ?give reason?​

Answer 1

Chemical Reactions That Make the Statue of Liberty Green.

copper reacts with air to form verdigris, but the Statue of Liberty is its own special color because of its unique environmental conditions. It's not a simple single reaction between copper and oxygen to produce a green oxide as you might think. The copper oxide continues to react to make copper carbonates, copper sulfide, and copper sulfate.

There are three main compounds that form the blue-green patina:

Cu4SO4(OH)6 (green)

Cu2CO3(OH)2 (green)

Cu3(CO3)2(OH)2 (blue)

Here's what happens: Initially, copper reacts with oxygen from the air in an oxidation-reduction or redox reaction. Copper donates electrons to oxygen, which oxidizes the copper and reduces the oxygen:

2Cu + O2 → Cu2O (pink or red)

Then the copper(I) oxide continues to react with oxygen to form copper oxide (CuO):

2Cu2O + O2 → 4CuO (black)

At the time the Statue of Liberty was built, the air contained a lot of sulfur from air pollution produced by burning coal:

Cu + S → 4CuS (black)

The CuS reacts with carbon dioxide (CO2) from the air and hydroxide ions (OH-) from water vapor to form three compounds: 2CuO + CO2 + H2O → Cu2CO3(OH)2 (green)

3CuO + 2CO2 + H2O → Cu3(CO3)2(OH)2 (blue)

4CuO + SO3 +3H2O → Cu4SO4(OH)6 (green)

The speed at which the patina develops (20 years, in the case of the Statue of Liberty) and color depends on the humidity and air pollution, not just the presence of oxygen and carbon dioxide. Patina develops and evolves over time. Nearly all the copper in the Statue is still the original metal, so the verdigris has been developing for over 130 years