Why is the Statue of Liberty Green? – Copper Chemistry!

The Statue of Liberty is an iconic landmark situated in New York, America. When asked to describe the appearance of the Statue of Liberty, what first things pop into your head? A woman, A torch, green?

So why is the Staute of Liberty Green?

Some simple Copper chemistry will help us to find out.

What you need:

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Vinegar

Salt

Small bowl

Copper coins

Method:

1. Put about a teaspoon of salt into a bowl

2. Add about 50mls of vinegar and stir to dissolve the salt.

3. With one coin, dip half in for a few seconds – lift out. What do you notice happen.

(You find that the dulness to the coin starts to go)

4. Put your coins into the solution and leave for 3-5 minutes

5. Take them out and compare to other dull copper coins!

You now have sparkling copper treasure!

The science bit

The reason copper coins dull in the first place, is because copper reacts with oxygen in the air and form a layer of copper oxide which is a dull greenish-grey colour. When you mix the salt (sodium chloride) with the vinegar (acetic acid) you form Sodium acetate and Hydrogen chloride. Hydrogen chloride is a very strong acid and this works well at rapidly cleaning the surface of the copper coin leaving it beautifully shiny and removing the oxide.

If left exposed to the air again , it will quickly react to form the dull greenish copper oxide layer.

The Statue of Liberty is coated in a thin layer of copper which has turned green due to reactions with air and water.

This explains why the Statue of Liberty is green!