Why is Lady Liberty Green?

Goal:

Students will recognize that oxidation is a chemical change that occurs as certain material is exposed to oxygen.

Materials:

  • Penny that has developed a patina
  • ½ cup vinegar
  • 2 teaspoons salt
  • Small bowl
  • Image of the Statue of Liberty
  • Penny without a patina
  • Paper towels

Procedure:

Show the students a penny that has developed a patina. 

Who can tell me what this object is?

What material is it made of?

Why does it appear to be dirty?

 

Explain to the students that it is a penny that has developed a patina.  It is sometimes called verdigris. The process of developing a patina is a chemical change called oxidation. When some materials, such as copper, are exposed to oxygen over a period of time they form a new substance. In the case of the penny, the new substance is copper oxide. 

Show the students an image of the Statue of Liberty.  Ask the students to share what they notice about the color of the Statue of Liberty.  Explain that because the Statue of Liberty is made out of copper and is located on an island in a large body of salt water (Atlantic Ocean), she has developed a coating of copper oxide. This chemical change is the reason that she is green. 

Ask the students what they think might happen if you drop the clean penny into a small bowl of salt/vinegar solution.  Record the students’ responses on the board.

Mix the vinegar and the salt in the bowl. Place the copper penny in the salt/vinegar solution. After a few minutes, remove the pennies and place the pennies on a paper towel. Do not rinse the pennies.

Have students record observations of any changes they observe.

 Explain that the residue left on the penny from the salt/vinegar solution reacts with oxygen to form the patina. 

Monitor the penny throughout the day, recording any changes.

Assessment:

Students will keep a journal to record observations of any changes.

 

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