Pennies are made from copper or copper and zinc. They look dull or dirty when covered with copper oxide which is formed when it reacts with oxygen in the air.
Kaine Painter, Redwood
The pupils started with the dirtiest pennies they could find and made predictions as to what would happen if they put them into a solution made of white vinegar and salt. The vinegar created an acetic acid and the sodium chloride of the salt was added to produce sodium acetate and hydrogen chloride which stripped the copper oxide from the coins and made them shiny!
The children then attempted to turn the pennies from shiny to green. The shiny pennies now have exposed copper which reacts with the oxygen in the air to form a layer of copper oxide again. As the pennies continued to react with the oxygen, a green-blue compound called malachite formed!
I really enjoyed this experiment, it allowed us to understand why the Statue of Liberty is green! Originally, it as copper coloured but that reacted with oxygen to form malachite.
Isaac Wright, Redwood
Have a look at the results below...
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