Environmental Education in the Schools (Peace Corps, 1993)
 Activities, activities and more activities

### Acid tests

 OBJECTIVES: Give an example of an acid and a base. Explain why some soils are not affected by acid rain as much as others. Describe how acid rain can affect plants, animals, and buildings and other structures. Discuss some methods that can help reduce the effects of acid rain. AGES: Intermediate, advanced SUBJECT: Science MATERIALS: Chalkboard or easel paper, copies of the demonstration on pages 236 and 237 (see demonstrations for additional materials)

Your kids can do some demonstrations to learn about how acid rain affects the environment. Start the activity by explaining to the kids how acid rain forms (see the background information in NatureScope-Pollution Problems and Solutions). Then give each person a copy of "Acid Demonstrations" on pages 236 and 237. Tell the kids that by doing several demonstrations, they'll learn more about the effects of acid rain. The first demonstration will help them learn about the pH methods that can help reduce scale.

Explain that the pH scale is a simple way to measure the relative acidity of a substance. The scale ranges from O to 14. A solution with a pH of 1 is very acidic, while one with a pH of 12 or 13 is very basic, or alkaline. A solution with a pH of 7 is considered neutral. For example, rain water, which is normally slightly acidic, averages between 5.0 and 5 6 The pH scale is logarithmic, which means that there is a tenfold difference between numbers- A solution that has a pH of 4 is about 10 times more acidic than a solution with a pH of 5.

Also explain to the kids that they'll be using specially treated pH paper to measure the acidity of different liquids. When they dip the paper into a liquid, it will turn a certain color. They should immediately match this color to a color chart to find out the pH. You might want to take the pH of one of the liquids listed in demonstration 1 (on page 236) as a group to make sure the kids understand how to use pH paper. (Note: Although pH paper is not the most accurate measurement of acidity, it does measure relative acidity, which is what's important for these demonstrations.)

Next divide the kids into small groups and have them do demonstration 1. Afterward copy the names of all the test solutions on a chalkboard or sheet of easel paper and have the groups fill in their results so the kids can see what the other groups came up with. Then, once the kids understand the pH scale, have them tackle the other demonstrations. You may want to have the kids work in teams to do all the demonstrations, or you can have the members of each team do one demonstration and later explain their results to the group. Also have the kids write down their answers to "What Happened?" and "Think About It" so they can discuss each demonstration later. See the information under "Acid Test Follow-up on pages 238 and 239 to add to your discussion. You might also want to have the kids point out the control in demonstrations 2-5.

SUPPLY TIPS

* You can order pH paper from biological supply companies, including Carolina Biological Supply, 2700 York Rd., Burlington, NC 27215, 800-334-5551. Be sure to order wide- range (1-12 or 0-14) pH hydrion paper. You'll need 4 or 5 rolls for a group of 25.

* You can get powdered lime, potting soil, and sphagnum moss at nurseries and garden stores. Be sure that the potting soil you get has a pH of around 6. You might want to buy a soil pH test kit to check the pH of the potting soil.

* Be sure to buy chalk that has calcium carbonate in it.

* Use reusable or recyclable containers for the demonstrations.

SAFETY TIP

* Caution the kids to avoid getting the powdered lime near their eyes or mouth. Also be sure to have them wash their hands after doing the demonstrations.