A fun science activity to celebrate Presidents' Day.

President Lincoln's birthday:      February 12^th. 1809

Clean up President Lincoln pennies for his birthday!

This is a fun experiment that you can do in class or set as a weekend challenge before Presidents Day:
 Clean old and dirty Lincoln pennies and explore some of the properties of metals.

Pennies get dull over time because the copper in the pennies slowly reacts with air to form copper oxide. Pure copper metal is bright and shiny, but the oxide is dull and greenish. When you place the pennies in the salt and vinegar solution, the acetic acid from the vinegar dissolves the copper oxide, leaving behind shiny clean pennies.

You need:

•  Dirty Lincoln pennies
• 1/4 cup white vinegar (dilute acetic acid) and 1 teaspoon salt (NaCl)
• 1 shallow plastic bowl
• water and paper towels

This is what you do:

1. Pour the salt and vinegar into the bowl and stir until the salt dissolves.
2. Dip a penny halfway into the liquid and hold it there for 10-20 seconds. Remove the penny from the liquid. What do you see?
3. Place the rest of the pennies into the liquid.
4. What happens?
5. Leave the pennies in the liquid for 5 minutes.

(Keep the liquid you used to clean the pennies, so don't dump it down the drain!)

• After 5 minutes, take half of the pennies out of the liquid and place them on a paper towel to dry.
• Remove the rest of the pennies and rinse them well under the tap.
• Place these pennies on a second paper towel to dry.
• Wait an hour then take a look at the pennies you have placed on the paper towels. (Write labels on your paper towels so you will know which towel has the rinsed pennies.)

v  Rinsing the pennies with water stops the reaction between the salt/vinegar and the pennies.

v  They will slowly turn dull again over time, but not quickly enough for you to watch!   

v  The salt/vinegar residue on the unrinsed pennies promotes a reaction between the copper and the oxygen in the air.

v  The resulting blue-green copper oxide is called 'verdigris'.