Download How well do different chemicals clean pennies?

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STARBASE Challenge: Polishing Pennies – Change Your Change!
This challenge is all about physical and chemical changes. You will use the activity below and the materials
provided to learn more about how we use physical and chemical changes in everyday life. During this activity,
you will take dull, dark pennies and try to make them shiny again with household chemicals. Your goal is to
determine which chemical is the best cleaner and correctly identify which changes are physical and which are
chemical. Remember, a physical change means a change in state or appearance (molecules stay the same)
while a chemical change happens when a new substance is formed (molecules change). You will need to bring
back the materials and the completed questions to receive a bead. You can earn an extra bead by bringing in a
picture or recording a video of you doing this activity and/or by having a family member sign your challenge!
Your STARBASE Kit should include:

Dull pennies
Acids – lemon juice, vinegar, cola (like Coke or Pepsi)
Bases – Dilute liquid dishwashing detergent
(¼ teaspoon detergent in 1 cup of water), baking
soda dissolved in water, crushed antacids dissolved
in water
At home you will need:







At least one acid
At least one base
Water
At least three small cups or containers
Spoon
Clock or timer
Paper towels
Background Information
Although pennies are made of bright and shiny copper metal, over time
they often tarnish, and become a darker, duller color. This color change
happens as the copper slowly reacts with oxygen in the air over time to
create copper oxide. The Statue of Liberty and many other landmarks
and historical artifacts started out copper brown and have changed to a
blue/green or darker brown over time. You may have even seen these
colors appear on pipes or in water fountains.
In order to keep copper materials shiny or clean them up, we will test
out two different types of chemical cleaners – acids and bases. You will
need to use at least one acid and at least one base, plus water to try
to clean your pennies. Choose from the list above. If you want to try
something that isn’t on the list, look at the ingredients list on the label
for the words “acid” for acids and “carbonate” or “soda” for bases.
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Procedure
1. Put a paper towel down on the table. Spread out the cups you are using on the paper towel.
2. Label the cups with the chemicals you are testing by writing the name of each chemical on the paper towel.
Vinegar
3.
4.
5.
6.
7.
8.
9.
10.
11.
Cola
Water
Baking soda
Dish soap
Place a penny inside of each cup and record your observations in the data table under “Before adding liquid”.
Pour enough of each chemical into the labeled cup to cover the penny.
Wait at least 5 minutes.
Use a plastic spoon to remove the penny from the first cup and observe how it looks. Write your observations in
the data table in the box under “After removing from liquid”.
Polish the penny with a paper towel. Observe what happens and write your observation in the table under
“After rubbing on paper towel”. Look at the paper towel. What color is the material that you rubbed off?
Place the penny on the work surface in front of the cup from which it was removed.
Repeat steps 6–8 for each of the pennies in the other liquids, and record your observations in the table.
Wait about 5 minutes after all pennies are out of their solutions and observe them again. Write down your
observations in the table under “After 5 minutes”.
Thoroughly clean the work area and wash your hands. Rinse the pennies with water, and dry them. Pour all
liquids down the drain, and place the other materials in the trash.
How well do different chemicals clean pennies?
Chemical Cleaner in the Cup – Write the name of the chemical and circle whether it is an ACID or BASE
Penny
Before adding liquid
After removing
from liquid
After rubbing on
paper towel
After 5 minutes
Water
ACID
BASE
ACID
BASE
ACID
BASE
ACID
BASE
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Questions
1. Leaving the penny in an acid like lemon juice, vinegar, or cola caused a
change
because
2. Drying the penny on a paper towel was a
change because
3. Based on your experiment, which of the chemicals was the best cleaner?
Why do you think this was the best cleaner?
4. What other chemicals do you think would work well to clean pennies?
Why did you choose these chemicals?
BONUS!
Use the key to decide which change is physical and which is chemical.
A.
B.
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Adapted from http://www.acs.org/content/dam/acsorg/education/whatischemistry/scienceforkids/chemicalphysicalchange/chemicalreactions/polishing-pennies.pdf