Ready-made science week

Chemical change

Main activity

• Show the class a shiny new copper coin and an older dull and dirty-looking copper coin.
• Place the dull coin in a beaker of pure lemon juice for about five minutes.
• Remove the coin. What has changed?
• The coin is dull because oxygen in the air slowly changes the shiny copper surface to a dull copper oxide. The lemon juice contains a weak acid which reacts with the copper oxide and removes it, changing the surface to shiny copper again.