Science project

Cleaning Coins

Research Questions:

  • Do the coins become clean or do they remain tarnished or oxidized?
  • Which cleaning solution works best?
  • How much effort does it take?
  • Do the copper pennies get cleaner than the other coins?
  • Do the oxidized coins get cleaner than the tarnished coins?


  • Six pennies (tarnished or oxidized)
  • Six nickels (tarnished or oxidized)
  • Six dimes (tarnished or oxidized)
  • Six quarters (tarnished or oxidized)
  • One cup dish liquid
  • One cup lemon juice
  • One cup orange juice
  • One cup water
  • One cup cola
  • One cup baking soda paste (Mix baking soda with water for a paste consistency.)
  • 24 cups
  • Six plastic spoons
  • Six toothbrushes
  • Newspaper or art cloth (to cover the table)
  • Latex gloves (optional)

Experimental Procedure:

  1. Fill four cups each one quarter full with each of the six cleaning solutions suggested (4 with lemon juice, 4 with orange juice, 4 with cola, 4 with water, 4 with baking soda paste and 4 with dish liquid). Label the cups.
  2. Carefully record each coin’s condition prior to placing it into its cup.
  3. Place one of each type of coin into each solution.
  4. Let all coins soak overnight.
  5. Using the plastic spoons and latex gloves, scoop each coin out of its cup and place it on the covered table. Take care to label and keep track of which coin came from which solution.
  6. Examine the coins and record what you see before you start using the toothbrushes.
  7. Use the toothbrushes to clean the coins, rinse with water, re-examine the coins, and record your observations.
  8. Address the research questions.

Terms/Concepts: oxidation, tarnish, chemical

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