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Experiment 2


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Acid/Metal Interaction

When acids and metals come in contact with each other, the metal is gradually dissolved away in a chemical reaction. In this experiment you will observe this reaction for yourself, but you will need patience. Even though the reaction starts as soon as the acid contacts the metal, the chemical effect of acids on metals may take at least five days for the human eye to see.


  • pH paper and color chart
  • 2 small, clear glasses
  • 2 clean copper pennies (use pennies minted before 1983)
  • white vinegar or fresh-squeezed lemon juice
  • distilled water
  • plastic wrap


  1. Label one glass “water” and the other “vinegar” or “lemon juice” depending on which acid you use.
  2. Place one penny in each glass. Be sure to use pennies minted before 1983 because pennies minted after that time have a different chemical composition.
  3. Barely cover one of the pennies with either vinegar or lemon juice.
  4. Dip a strip of pH paper into the vinegar, or lemon juice, for about 2 seconds, compare with the color chart, and record the result.
  5. Add enough distilled water to the glass labeled water to barely cover the other penny.
  6. Dip a strip of pH paper into the distilled water for about 2 seconds and compare with the color chart.                                                                                                                                                                              **If the pH is below 6, add a tiny amount (less than 1/8 teaspoon) of baking soda, or a drop of ammonia, and recheck the pH. Repeat this process until the pH is between 6 and 7. 
  7. Record the pH of and the appearance of each liquid.
  8. Seal the top of each glass with plastic wrap to prevent evaporation.
  9. Place in a safe, dry place for about 5 days.
  10. On day 5, observe the changes in appearance that occurred in each glass and take a new pH reading in each glass.  Record this data.
  11. At the end of the experiment, wash off the pennies with water, and pour the contents of the glasses down the sink (do not drink).



Day 1

Day 5

pH of water




Appearance of water





pH of vinegar




Appearance of vinegar







1.  What change, if any, took place in the water glass after 5 days?


2.  What change, if any, took place in the vinegar (or lemon juice) glass after 5 days?


3.  Over time one of the liquids should have become more neutral in its pH.  What substance caused this change?


4.  When you rinsed off the pennies, were you surprised that they both looked about the same as they did at the beginning of the experiment (assuming you used clean pennies)?


5.  Were there any physical changes, chemical changes, or both observed in either glass?  Be sure to explain what observations made this decision for you.


6.  Explain why one set up created a reaction but the other did not: (hint: think about the variable in this experiment)