Copper pennies always appear very dull even though copper metal is naturally much brighter. In the experiment we will find out why pennies look so dull and the best way to clean them.
You will need
- Some dull looking pennies
- Small bowls or pots
- Kitchen roll
Keep a few pennies out of the vinegar solution so that you can compare the colour of the treated pennies to those not treated.
- Place about 60ml of vinegar into a small glass and dissolve one to two teaspoons of salt into it.
- Place some pennies (keeping some out) into the solution so they all have good contact with the liquid and wait 5 minutes.
- After 5 minutes check your pennies and see if they are looking cleaner. Replace them into the solution if you would like them to be shinier.
- When you are happy with the result, wash the pennies with clean water and dry off with some kitchen towel
- Try using some lemon juice and salt in the same proportions to clean some pennies. Is It any better than vinegar?
- Ketchup is also known to have cleaning properties. Place some pennies into a small pot of ketchup for 5 minutes and see how the coins look.
- Add more pennies to the vinegar and salt solution and after 10 seconds, remove them and leave them on some paper towel dry. Overtime the pennies will go a greeny-blue colour. This chemical is called Malachite and is what is covering the copper Statue of Liberty in NYC. This forms when the oxygen and chlorine from the salt react with the copper.
Pennies are made of copper which is a bright orange red colour. Copper is a highly reactive metal which means it combines with oxygen and other impurities in the air and in the environment. When it does, it forms copper oxide on the surface which is what gives the pennies the very dull brown colour. The combination of the vinegar (a weak solution of acetic acid) and table salt (sodium chloride) helps to remove the copper oxide which has formed on the surface of copper coins bringing their true shine back.