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Acid Rain Experiments – Experiment 8 – Observing Buffer in Lakes, Ponds, and Streams

In this experiment you will observe the effects of limestone on the acidity of water. Some areas of the nation have a lot of limestone in lake bottoms and in soil, which helps neutralize the effects of acid rain. Crushed limestone is sometimes added to lakes, ponds, and other aquatic areas to help neutralize the effects of acid rain, thus preserving important aquatic systems until the source of acid rain can be reduced. Crushed limestone is easily obtained from local lawn and garden stores or nurseries.

Materials

Instructions

  1. Label one bowl vinegar; the other one vinegar plus limestone.
  2. Pour 1/4 cup crushed limestone into one bowl.
  3. Pour 1 teaspoon of vinegar into 2 cups of distilled water, stir well, and check the pH with either pH paper or a garden soil pH testing kit. The pH of the vinegar/water mixture should be about 4. If it is below pH 4, add a sprinkle of baking soda, stir well, and recheck the pH; but if it is above pH 4, add a drop or two of vinegar and again recheck the pH.
  4. Pour about 1 cup of the vinegar/water mixture over the limestone in the cereal bowl and stir with a clean, dry spoon.
  5. Pour the remaining vinegar/water mixture into the other cereal bowl.
  6. Check the pH of the vinegar/water mixture over the limestone and record it.
  7. Cover each bowl with plastic wrap to prevent evaporation.
  8. Every day for 6 days, stir the contents of each bowl with a clean, dry spoon and about 4 or more hours later (after the limestone has settled), test the pH of the water mixture in each bowl and record the result.

Questions and Answers

Did the pH of the vinegar/water mixture over the limestone become more or less acidic during the 6-day period? Why?

The water mixture should have become less acidic, changing from about pH 4 to as much as pH 6, depending on the water content of the limestone you used.

Does crushed limestone buffer the acid?

Yes, by neutralizing it.

Did the pH of the vinegar/water mixture in the other bowl (without limestone) change during the 6-day period?

The pH of the bowl without limestone should not have changed.


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