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Acid Rain Experiments – Experiment 9 – Looking at Acid Effects on Metals

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. The chemical effect of acids on metals may take at least five days for the human eye to see, even though the reaction starts as soon as the acid contacts the metal.

Materials

Instructions

  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. Or use a garden soil pH test kit.
  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. Or use a garden soil pH test kit. 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. Record the pH of the water.
  7. Seal the top of each glass with plastic wrap to prevent evaporation.
  8. Place in a safe, dry place for about 5 days.
  9. After about 5 days, observe the changes that occurred in each glass.
  10. 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).

Questions and Answers

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

There should be no change.

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

The liquid should be bluish-green. The bluish-green substance in the vinegar, or lemon juice, comes from the copper in the penny. It is a byproduct of the chemical reaction in which the acid in the vinegar, or lemon juice, very gradually eats away the penny.

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)?

The chemical reaction between the acid and the copper penny is so slow that you cannot see any difference in the shape of the metal in just 5 days, at least not with your eye alone. You may see some changes after about two weeks, especially at the edge of the penny.


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