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Acid Rain Experiments – Experiment 1 – Measuring pH

This experiment will illustrate how to measure the approximate pH of chemicals in water using a pH indicator. A pH indicator is a chemical that changes color when it comes in contact with acids or bases.

Materials
• pH paper and color chart (pH range 3 to 12) or garden soil pH testing kit
•distilled water (available at grocery stores and drug stores)
• white vinegar
• household ammonia (or baking soda)
• 3 small, clear cups or glasses
• 3 stirring spoons
• measuring cups and spoons (1/2 cup, 1/4 and 1 teaspoon)
• notebook and pencil

Instructions1. Rinse each cup with distilled water, shake out excess water, and label one cup vinegar, the second cup ammonia, and the third cup water.
2. Pour 1/2 cup distilled water into each of the 3 cups.
3. Add 1/2 teaspoon white vinegar to the vinegar cup and stir with a clean spoon.
4. Add 1/2 teaspoon ammonia to theammonia cup and stir with a clean spoon.
5. Do not add anything to the water cup.
6. Dip an unused, clean strip of pH paper in the vinegar cup for about 2 seconds and immediately compare with the color chart. Write down the approximate pH value and set the cup aside. (If using a garden soil pH tester kit, pour 1/4 teaspoon of the contents of the vinegarcup into the test container, and add 1/4 teaspoon of the test solution. Cover the test tube and shake once or twice to mix, or stir if necessary. Compare with the color chart provided in the kit, and record the result.)
7. Dip an unused, clean strip of pH paper in the ammonia cup for about 2 seconds and immediately compare with the color chart. Write down the approximate pHvalue and set the cup aside. (If using a garden soil pH tester kit, repeat the same process in step 6 using the contents of the ammonia cup instead of the vinegar cup.)
8. Dip an unused, clean strip of pH paper into the water cup for about 2 seconds and immediately compare with the color chart. Write down the approximate pH value. (If using a garden soil pH tester kit, repeatthe same process above using the contents of the water cup instead of the ammonia cup.)

Questions and Answers

Is vinegar an acid or a base?

Vinegar is an acid, and in this experiment it will display a pH of about 4. Vinegar at pH 4 turns pH paper yellow and most other pH indicators red.

Is ammonia an acid or a base?

Ammonia is a base and in this experiment it will display a pH ofabout 12. Bases turn most pH indicators blue.

Were you surprised to find that the distilled water did not have a neutral pH?

Pure distilled water would have tested neutral, but pure distilled water is not easily obtained because carbon dioxide in the air around us mixes, or dissolves, in the water, making it somewhat acidic. The pH of distilled water is between 5.6 and 7. To neutralizedistilled water, add about 1/8 teaspoon baking soda, or a drop of ammonia, stir well, and check the pH of the water with a pH indicator. If the water is still acidic, repeat the process until pH 7 is reached. If you accidentally add too much baking soda or ammonia, either start over or add a drop or two of vinegar, stir, and recheck the pH.

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