Quality Core Curriculum Objectives:

HS  Biology  #1 – Uses terms and processes employed in scientific research

                        #2 – Uses reference sources appropriately.

#26 – Assesses man’s impact on the environment/explore ways to help solve

ecological problems.

Students Will:

1) explain why some soils are not affected by acid rain as much as others.

2) describe how acid rain can affect plants, animals, and buildings and other structures

3) discuss some methods that can help reduce the effects of acid rain.

Activity #1 “To grow or not to grow”

Materials:  pH paper, seeds (radish, clover, pear, or mustard seeds) 1 large container, distilled water, 20 empty pint milk cartons, potting soil, marker, masking tape, vinegar, ruler, measuring cup

Procedure:

1.   Fill the 20 milk cartons three-quarters full with potting soil.  Plant one seed in each carton.

2.   Label 10 of the cartons with “A” for acid and 10 with “DW” for distilled water.

3.   Make a solution with a pH of about 3 by mixing 1 cup of vinegar with 4 cups of distilled water.

4.   Measure the pH of the distilled water and record it.  Then water the seeds in the cartons labeled “DW” with distilled water and the seeds in the “A” cartons with the acidic solution.  Put the cartons in a sunny spot indoors.  Have the students develop hypotheses as to which seedlings will grow more and quicker.

5.   Over the next three weeks, water all the seedlings with the appropriate kind of water whenever they look dry.  Make sure you give each seedling the same amount of water.  Record the date each seed sprouts and also measure the heights of the seedlings every few days.

6.   Which of the seedlings grew the most?  Which grew the least?  Why was it important to keep the seedlings indoors instead of letting them grow outside?  Why do you think you were told to water more than one seed with each solution?  If acid rain has about the same acidity as the acid solution you used, how might it affect plant growth?

Results:

The seeds watered with distilled water should have sprouted first and grown the most.  The seeds watered with the acidic solution should have sprouted later or not at all.  (If they sprouted, they might have had yellowed and/or stunted leaves).  The plants were kept inside to keep rainwater from affecting the results.  Watering several seeds with each type of solution provided a more representative sample and reduced the likelihood of any one seed skewing the results because of disease or other problems.  Point out to the students that the vinegar solution only simulated the acidity of acid rain.  Since vinegar contains substances that are not found in acid rain, the growth of the seeds may have been influenced by the other ingredients in the vinegar as well.   Also point out that acid rain is rarely as acidic as the solution used in this demonstration (acid rain generally has a pH of about 4). 

Scientists think that acid raid doesn’t significantly affect most crops, since these plants are exposed to the rain for a relatively short time and because the soil they grow in is usually limed to reduce acidity and fertilized to replenish nutrients.  But some scientists think that acid rain may affect trees (which are longer lived and can be exposed to acid rain for many years) by weakening them and making them more vulnerable to stress.  For example, acid rain may increase a tree’s susceptibility to drought, disease, cold, and insect attack.  Acid rain may also cause certain essential minerals in the soil to dissolve and wash out.  Without these minerals, a tree may grow more slowly.  These effects can be worsened when acid rain combines with other pollutants, such as ozone.

Activity #2:  “The Big Chill”

Materials: 2 ice cube trays, distilled water, lemon juice, freezer, pH paper, 2 containers, marker, masking tape, measuring spoon and cup

Procedure:

1.  Take the pH of the distilled water and record it.  Then pour enough distilled water into an ice tray to make 3 ice cubes.  Label the tray “DW” and put it in the freezer.

2.  Add 1-½ teaspoons of lemon juice to 2/3 cup of distilled water to make a solution with a pH of 3.  Pour enough of this solution into an ice tray to make 3 ice cubes.  Label the tray “A” for acid and put it in the freezer.

3.  Once the ice cubes have formed, pour 3 cups of distilled water into each container.

4.   Put the 3 distilled-water ice cubes into one of the containers and let them melt.  Then put the 3 acidic ice cubes into the other container and let them melt.  After the ice cubes melt, stir both solutions, then take the pH of both and record the results.  What were the results?  Were they as you predicted?

Results: 

The pH of the water should have become lower after the acidic ice cubes melted.  Explain to students that this activity replicated what happens in many parts of the world where acid snow falls in the winter.  In early spring, the snow that has fallen throughout the winter melts and runs into lakes and streams.  The surge of acidic water from sudden snowmelt can cause a drastic drop in pH.  This sudden jump in acidity (called “spring shock”) can kill certain species of fish.  Spring shock also interferes with the reproduction of fish and other aquatic animals.  For example, most fish, salamanders, and frogs lay their eggs in the early spring – just about the time spring shock occurs.  The eggs and young of these species are very sensitive to acidity and are often killed by the sudden increase in acidity.  If the eggs survive, the young that hatch may be deformed.

Activity #3:  “Soil Matters”

Materials:  sample of soil from your area, potting soil, sphagnum moss, powdered lime, funnel, filter paper, vinegar, distilled water, measuring cup, large container, pH paper

Procedure:

1.   Make up a solution with a pH of about 3 by adding 1 cup of vinegar to 3 cups distilled water.  Record the pH.

2.   Put a piece of filter paper into a funnel, and then fill the funnel about two-thirds full with the sphagnum moss. 

3.   Put the funnel over a large container, and then pour the acidic solution into the funnel (make sure you don’t add too much liquid all at once).  Wait until all the liquid has collected in the container below the funnel.

4.   Take the pH of the liquid that collects in the container.

5.   After rinsing out the funnel and container and removing the used filter paper, repeat the experiment twice using potting soil instead of sphagnum moss and then using the soil from your area.  (Be sure to rinse the equipment between uses).

6.   Did the pH of the liquid change after you poured it through the sphagnum moss?  The potting soil?  The soil from your area?  What do you think would happen if you added a small amount of lime to the soil from your area, and then poured some of the acidic solution through it?   In some areas where acid rain falls, lakes and streams don’t show the effects of acid rain.  But in other areas where acid rain falls, lakes and streams have become acidified.  Based on the results of this demonstration, why do you think these differences exist?

Results:

The pH of the solution poured through the sphagnum moss should have stayed the same.  The solution poured through the potting soil should have become less acidic.  Results for the soil taken from your area will vary, depending on the pH of your soil.  The potting soil, which is significantly less acidic than the solution, acted as a buffer; it neutralized some of the acid in the solution.  The sphagnum moss is more acidic and didn’t neutralize the acids in the solution.  If the pH of the solution poured through the soil from your area remained the same, your soil is probably acidic; if the pH increased, your soil is probably alkaline.

If you added lime to your soil, the pH of the solution that drained through the funnel should increase.  That’s because adding lime to soil makes it more alkaline and helps it to neutralize the acidic solution.

Differences in soil types can help explain the varying effects of acid rain.  In areas with deep, alkaline soils, acidic rainwater slowly trickles through the soil and is neutralized before it reaches lakes and streams.  Other areas, such as some parts of New England and the Adirondacks, have thin, relatively acidic soils.  Acid rain quickly runs into lakes and streams without being neutralized.  Because of this, many lakes in these regions have become acidified.