Acid Raindrops Keep Fallin' In My Lake (Page 2 of 2) in pdf

JCE Classroom Activity: #50

Student Activity

Acid Raindrops Keep Fallin’ in My Lake

Normal rain has a pH of about 5.6. If the air is polluted by oxides of sulfur and nitrogen that result from the

burning of fossil fuels, these pollutants can cause the rain to become more acidic. When acid rain falls in a lake, it can

lower the pH of the lake water, causing problems for the plants and animals that live there. Do some lakes have a

natural protection against acid rain? Could we use chemistry to protect lakes from acid rain? In this Activity you will

make very simple models of lakes and see what happens when acid is added.

Try This

You need to prepare some solid samples for testing; your instructor will tell you how many to use. One solid sample

must be crushed chalk (low-dust, white) or lime, both of which are mostly calcium carbonate. Crush chalk by placing

a stick of it in a plastic bag, setting it on a sturdy surface, and tapping it with a hammer. Additional samples may

include clean sand, marble chips, local soil, gravel, or small stones.

You will need: small bowls, test tubes, and spoons or stirring rods (the number required of each of these three items

is the number of solid samples you will use plus two); marker; test tube rack; solid samples described above; vinegar;

distilled water; measuring spoons and cups or graduated cylinders; dropper; plastic wrap; and red cabbage indicator.

Red Cabbage Indicator

If your instructor has not prepared red cabbage indicator, you can make it using either of the methods below.

When you are not using it, store the indicator solution in a closed container in a refrigerator. If you cannot refrigerate

the indicator solution, you should make and use a new batch each day.

Place two or three torn red cabbage leaves in a blender. Add 1/2 cup (125 mL) of distilled water. Blend until the

leaves are well-chopped. Strain the juice through a coffee filter.

Place two or three torn red cabbage leaves into a heat-resistant container. Add distilled water until the leaves are

covered. Heat the mixture to boiling and boil until the liquid is dark blue or purple. Remove the leaves.

Activity Procedure

__1. Set several small bowls on a surface where they will not be disturbed. Label one bowl “water”, another “water and

vinegar”, and the remaining bowl(s) with the name of the sample(s) you are using. Label the test tubes the same

way as the bowls.

__2. To the bowl(s) labeled with the name of a solid sample, add enough of the sample to

cover the bottom of the bowl with a thin layer of solid.

__3. Add 1/2 cup (125 mL) of distilled water to each bowl. If the solid material in a bowl

gets disturbed, shake the bowl gently until the solid is evenly distributed.

__4. Stir each bowl with a clean spoon or stirring rod. Remove 1 teaspoon (5 mL) of liquid from each

of the bowls and place it in the test tube with the matching label. Add several drops of red

cabbage indicator to each test tube. Observe the colors and record them. After recording the

colors, empty the test tubes into a sink and rinse them with distilled water.

__5. Add 1/2 teaspoon (2.5 mL) of vinegar to each bowl, except the one labeled “water”. Stir each

bowl with a clean spoon or stirring rod.

__6. Repeat step 4 immediately. Repeat it again three more times: after 30 minutes, after 24 hours,

and after 48 hours. Observe and record the colors for each repetition. Between testing times,

cover the bowls with plastic wrap.

Questions

__1. Over time, what happens to the colors observed in each bowl? In which bowl(s) is a chemical reaction occurring?

How can/could you tell? Write the reaction(s) that are occurring in the bowl(s).

__2. How is this simulation like acid rain falling into a lake? How is it unlike acid rain falling into a lake? How could

the simulation be made more like acid rain falling into a lake?

__3. Low-dust chalk, limestone, and marble consist mostly of calcium carbonate. What happens when acid rain falls

into a lake with a limestone lakebed? How could limestone be used to reverse the detrimental effects of acid rain?

Information from the World Wide Web

(accessed Nov 2002)

EPA’s Clean Air Market Programs—Acid Rain.

The Green Lane: Acid Rain.

Acid Rain.

Acid Deposition and Precipitation.

What is Acid Rain and What Causes It?

This Classroom Activity may be reproduced for use in the subscriber’s classroom.

40B

Journal of Chemical Education • Vol. 80 No. 1 January 2003 • JChemEd.chem.wisc.edu

Acid Raindrops Keep Fallin' In My Lake Page 2

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