Chemistry Experiments You Can Do at Home


How can I use chemistry to make dull pennies shiny?

  • Surface chemistry
  • Oxidation reactions
  • A handful of dull pennies (10 will do)
  • 1 teaspoon table salt (sodium chloride)
  • ¼ cup white vinegar (acetic acid solution)
  • a small, non-metallic bowl
  • water
  • paper towels or napkins
  1. Pour ¼ of a cup of vinegar and 1 teaspoon of table salt into the bowl.
  2. Stir the mixture until the salt is completely dissolved.
  3. Try first dipping one penny into the solution for about 15 seconds and remove it. Do you notice a change in the part that you dipped into the solution?
  4. Place the remaining pennies into the solution. You will likely notice a visible reaction as the pennies are placed in the solution. The reason pennies eventually begin to appear dull is that the copper surface reacts with oxygen in the air to create a layer of copper oxide. In this experiment, the vinegar and salt will react with the copper oxide and remove it, which will leave a layer of the original shiny copper exposed on the surface.
  5. Allow the pennies to remain in the solution for several minutes. If necessary, try to move the coins around so as to expose both sides of each coin to the solution. If possible, flip the coins over after a couple of minutes.
  6. Drain the solution and rinse the coins with clean water. They should now look clean and shiny!

Copper pennies turn dull because they oxidize over time. A mixture of vinegar and salt reacts with the copper oxide to clean the pennies and make them shiny again. (Photo by Jim Fordyce.)


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