Lesson7 ~ --------"'

Overview

Biological and ag ricu ltu ral concepts

pH ... Potential Horrors of Acid Rain Assessing the effects of pH on the growth and development of Fast Plants

Part I: A buffering blanket of soil Part II: Germination-the first step Part Ill : Growth and development

Acid rain, a major environmental concern, results from high concentra­tions of sulfur pollutants in the atmosphere.

Different regions of the world and different areas in the U.S. experi­ence varying amounts of acid rain depending on the climate, geogra­phy, wind patterns and degree of industrialization. Acid rain concen­trations also vary from place to place due to the frequency of natural occurrences such as lightning and volcanic activity.

In this experiment, students will investigate interactions between soil and acid rain, and look at the germination, growth and development of plants in an acid environment.

Plant growth and development Water cycle Acids and bases Data collection and interpretation Soil science

Acid Rain I 7-1

Lesson 7

The teachable moment

Background

7-2 I Acid Rain

Teacher material

Both biology and agriculture teachers can use this activity in an plant or crop science unit. This activity can also illustrate the practice of data collection, data analysis and preparation of solutions. Biology teachers may find this activity useful for a unit in ecology, while an agriculture teacher may use it for a forestry or soils unit.

This activity may also be followed with discussion of what is being done to reduce the damage caused by acid rain, and what actions are being taken globally to reduce sulfur emissions.

The fundamental attraction to an issue such as global warming, defor­estation or acid precipitation is in the delivery or "packaging" pre­sented to students. This could take the form of a question: "How might taking a shower or turning on a light here in the United States kill fish in Sweden?" Adding an international perspective to the ques­tion provides a framework for further investigation. Students are motivated to challenge the notion that such profound relationships could exist. They begin to realize that their actions go far beyond the classroom activities they carry out. They are able to appreciate the complexity of the world they live in and formulate opinions regarding global sustainability.

While acid rain, snow, sleet or hail might not keep the postal carrier from delivering, they have been linked to changes in the ecosystems they fall on. Since acid precipitation is formed by interactions in the upper atmosphere, it can travel great distances and the effects can be far removed from the causes. The socioeconomic/ ethical implications of this are thus far-reaching and teachers are encouraged to pursue these avenues as support for the following lab.

The two major chemicals that make up acid rain are S02 (sulfur diox­ide) and NOx (nitrogen oxides, made up of NO and N02, nitric oxide and nitrogen dioxide). These pollutants have been produced naturally by volcanic action, decaying organic matter, lightning and sea spray. This relatively small amount of acid can be removed from the air through interaction with vegetation and the ocean. Pollutants from industry, car emissions, and the burning of fossil fuels are so great that natural processes of removing the acid cannot keep up.

Most acid rain is caused by the burning of high-sulfur fuels. When these fuels are burned, S02 (sulfur dioxide) is formed. S02 then reacts with the oxygen of the air, forming S03 (sulfur trioxide), which in turn reacts with the water vapor of the air, to form a sulfuric acid solution (~S04), or acid rain.

Lesson 7 Teacher material

Burning of coal S + 0 2 = S02 2S02 + 02 = 2S03 so3 + }\0 = }\S04

A pH scale designates the acidity of water in terms of the concentra­tion of H+ in solution. On a pH scale, the lower the number, the greater the acidity, the higher the number the greater the alkalinity. A pH of 4 is ten times as acidic as a pH of 5. A pH of 4 is 100 times as acidic as a pH of 6. Distilled water is neutral, having a PH of 7. Naturally occur­ring rainfall has a PH of 5.6. Acid precipitation often has a pH of 4.0-4.5 but has been observed as low as 1.5. Strong bases can reach a pH of 14.

Acid precipitation, which can carry acid in rain, snow, hail, sleet, fog or dew, was first observed in England in the 1600s when the country was deforested, wood became scarce and coal became the predominant energy source. The term "acid rain" was coined in 1872 by Robert Angus Smith, First Chief Alkali Inspector of the British Isles.

Acid precipitation can have a devastating impact on an ecosystem. Unfortunately, this serious impact is often subtle and indirect. Plants and trees exposed to acid rain are deprived of vital nutrients when calcium, magnesium, and potassium are leached from the soil. Alumi­num, abundant in the soil in a non-toxic form, changes to a toxic soluble form in the presence of acid. Hence one of the serious effects of acid precipitation on plants is aluminum toxicity.

As acidification becomes more severe, direct ecosystem effects begin to appear. Lakes with pH levels below 4.7 cannot support fish reproduc­tion. Tree damage from acid rain in the U.S. extends from the Adirondack Mountains in New York to the Appalachian Mountains in Georgia. Billions of dollars have been lost due to crop damage. Eco­systems in the Scandinavian countries, central Europe and eastern North America all suffer from acidification. Humanmade cultural attractions such as the Taj Mahal, the Sphinx, the Parthenon, and the cathedral in Cologne are also affected as they corrode and dissolve in the face of acid precipitation.

A common, though short-sighted, local solution to the acid rain prob­lem is to make smokestacks taller so that emissions are carried farther away. This is not a long-term solution in that emissions are simply carried to other areas and not eliminated. S02 is naturally taken out of the environment as it runs through soil and is acted upon by microor­ganisms. Tall smokestacks, erected to promote dilution of emissions,

Acid Rain I 7-3

Lesson 7

Teacher management

7-4 I Acid Rain

Teacher material

force emissions high into the air, allowing them to react for longer periods of time with oxygen in the air, increasing the problem.

There are three parts to this unit. Each part can be done separately.

• Part I : Buffering capacity of soil • Part IT : Effects of acid on plant germination • Part Ill : Effects of acid on plant growth and development

This experiment uses either acetic acid (C~C02H) or dilute sulfuric acid (~504), which in concentrated form, and if handled incorrectly, can be dangerous. Therefore, we recommend that a teacher prepare all the acid dilutions in advance. However, if this activity is used with more advanced students, you may want to have students prepare dilutions and in so doing teach the need for precise and accurate mea­surement and safe laboratory practices.

Preparing the solutions using concentrated sulfuric acid (H2S04):

You will need the following materials:

• six 2-liter bottles for dilutions • 500 or 1000 ml beaker • stirring rod • hotplate • pH paper, range 1-7 • tweezers

Directions:

1. Always add acid to water, not the reverse.

2. Stir each solution carefully. Rinse stirring rod, eye dropper and beaker after each use.

3. In using the dilution table below, note the following: • Create your solutions in the order indicated • To get the correct pH you may need to add slightly less or slightly more than the amounts indicated depending on the strength of your concentrated sulfuric acid.

Lesson 7

Sources for materials

Tips and safety

pH2

pH3

pH4

pHS

Teacher material

Volume needed:

• Part I (need 300 ml/ group) • Part IT (need 200 ml/per acid level tested)) • Part Ill (need 200 ml per group)

Total volume of Total Volume of 200-300mls 700mls (for Part I, II, or III) ( for Parts I, II and ill)

10 dr.}\504 /500 ml}\0 15 dr. ~504 /750 m1 ~0

40 dr. pH 2 soln /360 ml ~0 75 dr. pH 2 soln I 675 m1 ~04

40 dr. pH 3 soln /360 ml}\0 75 dr. pH 3 soln /675 m1 ~0

40 dr. pH 4 soln /360 ml}\0 75 dr. pH 4 soln /675 ml ~0

4. To make a pH 7.0, boil distilled water (which will have a pH about 5.6) for 5-10 minutes to remove dissolved C02 from water. Cover loosely to prevent C02 reabsorption, yet allowing steam to escape. Allow to cool 20 minutes.

5. Pour each solution into appropriately labelled 1-liter bottles. A plastic cap with many holes punched in it will convert this storage container into a sprinkling device for easier application of your acid solutions.

Bottles: redemption centers, your students, acquaintances, etc. Chemicals: Carolina Biological or other supply houses. Film canisters: film developing centers

1. Always add acid to water, never the reverse.

2. Safety goggles and lab aprons should always be worn when working with acids.

3. In case of acid contact with skin, flush area under cool water.

4. Heat sources such as a propane torch or Bunsen burners should be carefully supervised by the teacher if not actually used by the teacher in ad vance.

Acid Rain I 7-5

Lesson 7

Key terms

References

7-6 I Acid Rain

Teacher material

5. Divide your class into groups of three to four. Each group will test a certain pH range. Test pH 2, 3, 4, 5 and 7. If you have enough students, test 4.5 and 5.5 also.

7. A class can do Parts I, TI and III singly. Part ill, growth and development, can be terminated after the flowers have finished flowering at two weeks or can be run to day 40 and total seed harvest can be calculated.

Acid: a chemical that produces excess H+ ions when dissolved in water

Acid Rain: atmospheric precipitation (rain, snow, fog, frost, sleet) that has a pH of less than 5. Dew is 30 times more acidic than any other form of precipitation

Dilution: lowering the concentration of a solution by the addition of water

pH: the measure of acidity or alkalinity

Solution: a homogeneous mixture of one or more liquids

Jacob, Anthony T., Acid Rain, (Madison, Wisconsin: University of Regents, 1991).

Corson, Walter H., ed., Global Ecology Handbook (Boston, MA, Beacon Press, 1990).

Steger, Will, and John Bowermaster, Saving the Earth (New York, NY, Alfred A. Knopf, Inc., 1990).

Canadian Embassy; Science News, Ontario Ministry of the Environ­ment, Pacific Northwest Laboratory, 1990).

Hinrichsen, Don, Acid Rain and Forest Decline, in Edward Goldsmith and Nicholas Hildyard (eds.), The Earth Report (Los Angeles: Price Stern Sloan, 1988), p. 67.

Whelpdale, D.M., "Acid Deposition: Distribution and Impact, Water Quality Bulletin, Vol. 8, 1983, p. 72.

Lesson 7

Introduction

Teacher management

Preparation

Activity time

Part 1: Teacher material

Part 1: A buffering blanket of soil

In this portion, students will explore the interactions between acid and soils. A soil's buffering capacity, that is its ability to neutralize an acid, is a significant factor in the effect that acid precipitation has on an ecosystem. Buffering capacity of a soil depends on the mineral make­up of the soil, the organic content and physical properties such as density and particle size. A solution of a given pH will usually be neutralized to some degree by contact with the soil. However, after prolonged contact with the acid, a soil will lose its buffering capacity. A more in-depth soils background can be found in the background section of Chapter 9 in this manual, "Down and Dirty, A study of water movement through soils."

In this experiment, students will examine and compare the buffering effects of one or more soils. Ideally, the soil should be collected locally. After the experiment, students should be encouraged to think about the ecosystems that provided the soil. What do their results say about the vulnerability of that ecosystem to acid precipitation?

If you want to examine different types of soil, results from a local soil survey, available through your local extension office or Soil Conserva­tion Service office, will be useful in selecting soil samples. Virtually every county in the U.S. has a completed soil survey map available for the asking. These reports map the soil types in local areas and describe how these soils will respond when used. A soil survey will explain the variability of soils from community to community and will describe the reasons for such variation. If local soils are unavailable, potting soils or potting mixes can be used. The buffering capacity of potting mixes is dramatic!

Day 1-build and set up columns Day 2- run experiment

Students can work in groups of one to three. Have at least six groups (to test pH 2, 3, 4, 5, 7 and distilled water). If there is an ample supply of soil and bottles, make the groups as small as possible. Each group will construct a column and run one pH solution through its column. Data Table #1, "Classroom pH Values," should be at the front of the room. Litmus paper results from each group should be recorded on that classroom data table.

Acid Rain I 7-7

Lesson 7

Safety and tips

Materials

7-8 I Acid Rain

Part 1: Teacher material

Use soils that are slightly damp but not dripping

Crush the dry soil samples to destroy any remaining soil structure.

Sand samples that are single grained rarely require this; however, you will need to process finer grained samples, like clays, in this manner.

If you want to work with a heavy clay sample, the experiment will probably take longer than two class periods to run. If that will cause scheduling problems, test your most finely grained sample to deter­mine if the experiment can be completed in two class sessions. If the sample is too heavy, mix in sand to a 3:1 ratio (3 parts fine-grained to 1 part sand).

Make sure that each column is constructed using two bottles of the same brand name since bottle size varies slightly.

If you are teaching a unit on soils, the number of soil types can be increased and the types more carefully determined.

Horticulture instructors may wish to demonstrate the properties of the components of professional soil mixes using this design.

For each group (1-3 students):

• 500 ml soil • two 2-liter bottles, one with cap • Exacto knife, razor blade or other cutting blade • grease pencil • scissors • 300 ml appropriate acid stock solution • graduated cylinder or bottle • tweezers • film can

For the classroom (only one set necessary):

• tape • hole punch • nail poke or awl • hot water or hair dryer

Lesson 7

Introduction

Part 1: Student material

Part I: A buffering blanket of soil

While acid rain, snow, sleet or hail might not keep the postal carrier from delivering, they have been linked to changes in the ecosystems they fall on. Since acid precipitation is formed by interactions in the upper atmosphere, it can travel great distances and the effects can be far removed from the causes. The socioeconomic/ ethical implications of this are thus far-reaching.

The two major chemicals that make up acid rain are S02 (sulfur diox­ide) and NOx (nitrogen oxides, made up of NO and N02, nitric oxide and nitrogen dioxide). These pollutants have been produced naturally by volcanic action, decaying organic matter, lightning and sea spray. This relatively small amount of acid can be removed from the air through interaction with vegetation and the ocean. Pollutants from industry, car emissions, and the burning of fossil fuels are so great that natural processes of removing the acid cannot keep up.

Most acid rain is caused by the burning of high-sulfur fuels. When these fuels are burned, S02 (sulfur dioxide) is formed. S02 then reacts with the oxygen of the air, forming S03 (sulfur trioxide), which in turn reacts with the water vapor of the air, to form a sulfuric acid solution (}\S04), or acid rain.

Burning of coal S + 0 2 = S02 2S02 + 02 = 2S03 so3 + }\0 = ~so4

A pH scale designates the acidity of water in terms of the concentra­tion of hydrogen ions in solution. On a pH scale, the lower the number, the greater the acidity, the higher the number the greater the alkalinity. A pH of 4 is ten times as acidic as a pH of 5. A pH of 4 is 100 times as acidic as a pH of 6. Distilled water is neutral, having a PH of 7. Natu­rally occurring rainfall has a PH of 5.6. Acid precipitation often has a pH of 4.0-4.5 but has been observed as low as 1.5. Strong bases can reach a pH of 14.

Acid precipitation, which can carry acid in rain, snow, hail, sleet, fog or dew, was first observed in England in the 1600's when the country was deforested, wood became scarce and coal became the predominant energy source. The term "acid rain" was coined in 1872 by Robert Angus Smith, First Chief Alkali Inspector of the British Isles.

Acid Rain I 7-9

Lesson 7

Materials

7-10 1 Acid Rain

Part 1: Student material

Acid precipitation can have a devastating impact on an ecosystem. Unfortunately, this serious impact is often subtle and indirect. Plants and trees exposed to acid rain are deprived of vital nutrients when calcium, magnesium, and potassium are leached from the soil. Alumi­num, abundant in the soil in a non-toxic form, changes to a toxic soluble form in the presence of acid. Hence one of the serious effects of acid precipitation on plants is aluminum toxicity.

As acidification becomes more severe, direct ecosystem effects begin to appear. Lakes with pH levels below 4.7 cannot support fish reproduc­tion. Tree damage from acid rain in the U.S. extends from the Adirondack Mountains in New York to the Appalachian Mountains in Georgia. Billions of dollars have been lost due to crop damage. Eco­systems in the Scandinavian countries, central Europe and eastern North America all suffer from acidification. Humanmade cultural attractions such as the Taj Mahal, the Sphinx, the Parthenon, and the cathedral in Cologne are also affected as they corrode and dissolve in the face of acid precipitation.

A common, though short-sighted, local solution to the acid rain prob­lem is to make smokestacks taller so that emissions are carried farther away. This is not a long-term solution in that emissions are simply carried to other areas and not eliminated. S02 is naturally taken out of the environment as it runs through soil and is acted upon by microor­ganisms. Tall smokestacks, erected to promote dilution of emissions, force emissions high into the air, allowing them to react for longer periods of time with oxygen in the air, increasing the problem.

In this experiment, you will examine and compare the buffering effects of one or more soils. Ideally, the soil should be collected locally. After the experiment, think about the ecosystems that provided the soil. What do your results say about the vulnerability of that ecosystem to acid precipitation?

For each group (1-3 students):

• 500 ml soil • two 2-liter bottles, one with cap • Exacto knife, razor blade or other cutting blade • grease pencil • scissors • 300 ml appropriate acid stock solution • graduated cylinder or bottle • tweezers • film can

Lesson 7

Procedure

For the classroom :

• tape • holepunch • nail poke or awl • hot water or hair dryer

Day 1 - Preparation

1. Mark one bottle at the base for cutting. Using an Exacto knife or razor blade, cut a small slit in the bottle and complete the cut with scissors. This will serve as the soil column.

2. Mark another bottle just below the shoulder and cut. This will be the column reservoir. You may also want to cut away the base allowing better viewing. A

Part I Student material

3. Using a hole punch, punch one hole in the bottle base, 2 to 4 em below the top. The hole allows air to escape from the reservoir when air is displaced by the pH solution entering the reservoir from the soil column above. (Be careful not to pour water out the hole later in the experiment!)

Acid Rain I 7-11

Lesson 7

7-12 I Acid Rain

Part 1: Student material

4. Use a nail poke to make several holes in the center of each of three caps. Try to make the holes identical in each cap. Place a film can over each cap. This will prevent water from flowing out too fast when you are initially saturating the column with the pH solution.

5. Place 500 mls of soil in the column.

6. Take an initial pH of your solution. If using litmus paper, hold the paper with tweezers. Tape the litmus paper on the class data table and record the initial pH.

7. Slowly, pour 300 mls of the appropriate pH solution on the column.

8. After one minute, carefully remove the film can from the bottle cap making sure not to unscrew the cap. Pour contents of the film can into the reservoir.

9. Replace the soil column on the top of the reservoir and let drain until most of the solution has passed through the column.

10. Take the pH of the solution that has drained through the column. Tape the litmus paper and record the pH on the classroom data tables.

A

Lesson 7 Part 1: Data sheet

Classroom pH Values

Solution Initial Final

II II I put I I put I

pH 2 I litmus I I litmus I 1 paper1 pH 1paper1 pH I here I I here I

I I I I

II II I put I I put I

pH 3 I litmus I llitmusl 1papeq pH 1 papeq pH I here I I here I

L J L J II II I put I I put I

pH 4 llitmusl llitmusl 1 papeq 1 papeq I here I pH I here I pH L J L J II II I put I I put I

pH 5 llitmusl llitmusl 1 paper1 pH 1 paper1 pH I here I I here I

I I I I

II II I put I I put I

pH 7 llitmusl llitmusl 1 paper1 I here I pH 1 papeq

I here I pH I I l J II II I put I I put I

Distilled water I litmus 1 llitmusl 1 paper I pH I paper! pH lhere I 1 here 1

I I I I

Acid Rain I 7-13

Lesson 7

Results and discussion

Extensions

7-14 I Acid Rain

Part I: Student material

1. Did the soil change the pH of the leachate?

2. What kinds of soil would be more likely to raise the pH of acid rain?

3. Graph the pH of the liquids versus the pH of the leachate for each of the acid concentrations.

1. Test different soil types such as sand1 loaml commercial potting mix or clay.

2. Mix varying amounts of sand with your soil and see how it affects the pH of the leachate.

3. Try adding various compounds to the soil such as crushed eggshells~ chalk or limewater. How does this change the acidity of the leachate?

4. Try adding organic matter such as leaves or grass to the soil. Test the leachate.

5. Consider changing the length of the soil column.

6. Do other acids of equivalent pHs interact with the soil in the same way as ~SO 4? Try vinegar or hydrochloric acid.

7. What is the pH of rain in your region?

Lesson 7

Introduction

Teacher management

Preparation

Activity time

Tips and safety

Materials

Part II: Teacher material

Part II: Germination-the first step

A mature seed consists of an embryo surrounded by a protective seed coat. The seed remains dormant until environmental conditions such as light, water, and temperature are right for germination. The quality of that water can have a tremendous impact on the germination pro­cess. In this experiment, you will examine the effects of a low pH solution on germination.

1/2 - 1 hour to gather material, after making the pH solutions.

One 50-minute class to set up experiment 5-10 minutes of observation and measurement for four days (If plants other than Wisconsin Fast Plants are used, germination might take longer.)

Students can work in groups of one to three. Have at least six groups (to test pH 2, 3, 4, 5, 7 and distilled water). Each group will test germi­nation for one pH solution. When considering the results, the entire class' data should be compiled and examined.

For each group (1-3 students):

• petri plate • 1 mm plastic grid paper circle • filter paper (9 em , No. 2) • 8 radish, turnip or Fast Plant seeds • magnifying glass • 200 ml of the appropriate pH solution (for direction for making the

acid dilutions, see page 7-5) • tweezers • water reservoir (a bottle bottom does well)

(if only one petri plate is going to be tested for each pH solution, two extra empty petri plates are needed for support in each reservoir)

Acid Rain I 7-15

Lesson 7

Introduction

Materials

Procedure

7-16 I Acid Rain

Part II: Student material

Part II: Germination-the first step

See introduction to Part I on page 7-9, and the following.

A mature seed consists of an embryo surrounded by a protective seed coat. The seed remains dormant until environmental conditions such as light, water, and temperature are right for germination. The quality of that water can have a tremendous impact on the germination pro­cess. In this experiment, you will examine the effects of a low pH solution on germination.

For each group (1-3 students):

• one petri plate • 1 mm plastic grid paper circle (see App. C, p. 16 for template) • filter paper (9 em , No. 2) • 8 radish, turnip or Fast Plant seeds • magnifying glass • 200 ml of the appropriate pH solution • tweezers • water reservoir (a 2-liter bottle bottom does well) • waterproof tape (black electrical tape works well)

(if only one petri plate is going to be tested for each pH solution, two extra empty petri plates are needed for support in each reservoir)

1. Place the plastic grid in the top of a petri dish.

2. Place the filter paper on top of the grid.

3. Moisten filter paper with the appropriate solution. Press out air bubbles trapped under the filter paper.

4. Place eight seeds along the top line of the grid as shown:

Petri plate

seeds

Lesson 7 Part II: Student material

5. Write your name, date and the pH of your solution on the cover of the petri plate.

6. Cover the dish and tape shut.

7. Tape the hole on the bottom of a 2-liter bottle bottom with water proof tape.

8. Place petri dish in a 2-liter bottle bottom. The petri plate can lean back slightly. If you are the only one testing your pH, prop the petri plate up with two other empty plates as shown.

Petri plates

9. Fill the bottle bottom with approximately 100 ml of the appropriate pH solution.

10. Place reservoir and petri plates under fluorescent lights.

11. Check the plates in 5-10 minutes to make sure the solutions have flowed into the petri plate. If not, twist the cover and jiggle the plates slightly to break a seal which may have formed.

Day 2, 3, and 4:

Observe the seeds and record the data on the data sheets. Add more pH solution, if necessary.

Acid Rain I 7-17

Lesson 7

Germination Observations

pH Level. ____ _

# of seed coats split

Day

Day

Day

pH Level ____ _

Seed Seed Seed #1 #2 #3

Day

Day

Day

7-18 I Acid Rain

# of embryonic roots emerged

Length (in mm)

Seed #4

Seed #5

Seed #6

Part II: Data sheet

observations

Seed Seed #7 #8

Lesson 7 Part II: Data sheet

Class Data Sheet

0/o Germination Average Average Root Length Shoot Length

pH 2

pH 3

pH 4

pH 5

pH 6

distilled water

Acid Rain I 7-19

Lesson 7

Results and discussion

Extensions

7-20 I Acid Rain

Part II: Student material

1. What first emerges from the seed?

2. Why do you think the seed coat splits?

3. What percent of seeds germinated?

4. What color is the shoot? the root? Does the color change?

5. Does pH affect germination? How?

6. What do your results tell you about the effect of acid precipitation on an ecosystem?

7. Can you think of other reasons beside pH which might have caused the seed not to germinate?

1. Compare the effects from various acids at the same pH.

2. Compare germination between different types of seed.

3. Try the activity using rainwater collected in your area.

Lesson 7

Introduction

Teacher management

Preparation

Activity time

Tips and safety

Materials

Part Ill: Teacher material

Part Ill: Growth and Development

How does acid precipitation affect plant growth and development? There are many aspects of growth and development that could be affected including height, development time, leaf size, number of flowers and root growth.

In this experiment, students will watch plants grow while enclosed in a bottle terrarium. Students will observe water that has evaporated and condensed on the inside of the terrarium. This water evaporates, condenses and rewaters the plants similar to the water in our own water cycle. Does the pH change as the water goes through the "water cycle?''

After preparation of the pH solutions, preparation of this experiment should take 1/2 - 1 hour to gather materials.

Construction: one or two class periods Setting up the experiment: one class period Observations: plants can be observed to flowering (about two weeks) or until seed harvest (about six weeks). During that time, the observa­tions can be as minimal or extensive as desired.

Students can work in groups of two to four. Have at least six groups (to test pH 2, 3, 4, 5, 7 and distilled water). Each group will construct a column and use one pH solution to water its plants. Classroom data should be compiled.

Make sure that each column is constructed using two bottles of the same brand name since bottle size varies slightly.

For each group (2-4 students):

• one 2-liter bottle • one 1- liter bottle • scissors • 350 mls soil • grease pencil

(continued)

Acid Rain I 7-21

Lesson 7

7-22 I Acid Rain

Part Ill: Teacher material

• Exacto knife, razor blade or other cutting tool • 200 ml appropriate acid stock solution (for directions for making

acid solutions see page 7-5) • 5 Fast Plant seeds • 30 mls of 20-20-20 liquid fertilizer (standard concentration)

For the classroom:

• waterproof tape (electrical tape works well) • nail poke or awl • hot water or hair dryer

Lesson 7

Introduction

Materials

Part Ill: Student material

Part Ill: Growth and development

See introduction to Part I on page 7-9, and include the following.

How does acid precipitation affect plant growth and development? There are many aspects of growth and development that could be affected including height, development time, leaf size, number of flowers and root growth.

In this experiment you will watch plants grow while enclosed in a bottle terrarium. You will observe water that has evaporated and condensed on the inside of the terrarium. This water evaporates, condenses and rewaters the plants similar to the water in our own water cycle. Does the pH change as the water goes through the "water cycle?''

For each group (2-4 students):

• one 2-liter bottle • one 1- liter bottle • one extra 1-li ter bottle base • scissors • 350 mls soil • grease pencil • Exacto knife, razor blade or other cutting tool • 200 ml appropriate acid stock solution • 5 Fast Plant seeds • 30 mls of 20-20-20 liquid fertilizer • sharp needle • 150-200 mls of Jiffy Mix potting soil

For the classroom:

• waterproof tape (electrical tape works well) • nail poke or awl • hot water or hair dryer

Acid Rain I 7-23

Lesson 7

Procedure

7-24 I Acid Rain

Part Ill: Student material

Construction of terrarium:

1. Remove the label and base of a 2-liter bottle.

2. Tape the holes of the base with electrical tape.

3. Cut bottle 2 em above the shoulder.

I

:~ based removed

4. With the sharp needle, punch approximately 100-150 holes in the bottom and sides of the bottle. (When inverted, this will be the top.)

5. By inverting the bottle and putting it into the base, you have the terrarium.

. . .. . . , ... · · .. : .. :: .... ·

./ ... / I / I

Lesson 7

Making the inner column:

1. Cut a delabelled 1-liter bottle 2 em below the shoulder.

2. Cut away the sides of the base.

3. With the sharp needle, poke 50-100 holes around the base of the bottle.

Part Ill: Student material

··-------·--- 4-- Cut

!~-Cut away the base

·/~'/'/% ~jf /,;/ ~-Extra base

l ) ~-Punch holes

4. With the awl, punch approximately 25 small holes in the bottom of an extra bottle base. Tape up the large holes with waterproof tape.

5. Assemble the construction as shown.

/ .

2-liter dome

+---1--+-- 1-liter bottle

Acid Rain I 7-25

Lesson 7

7-26 I Acid Rain

Planting the seeds:

1. Dampen the Jiffy Mix slightly. Fill the upper 1-liter base to the rim.

2. Water gently with distilled water until the water runs through.

3. Sow five Fast Plant seeds.

4. Cover lightly with a thin layer of potting soil.

5. Gently resaturate the soil with distilled water.

6. Add 10 drops of the appropriate pH solution.

Each day after planting:

1. Add 10 drops of the appropriate pH solution each school day for two weeks.

2. Add more water if the soil looks dry. It is very important not to let the plants dry out.

3. Record observations on data sheet, noting color, height and abnormalities.

4. Occasionally measure the pH of the condensation ("acid rain") on the inside of your terrarium.

5. When the plants grow too tall for the terrarium, take out the inner 1-liter bottle and cut it down until it lowers the plants sufficiently.

6. Fertilize with 5 mls of fertilizer on day 3 after planting, 12 mls on day 7, and 12 mls on day 14.

Lesson 7 Part Ill: Data sheet

Growth and Development Data Sheet

pH ___ _

Plant Plant Plant Plant Plant #1 #2 #3 #4 #5

Height (Day 7)

Height (Day 14)

Number of Flowers (Day 14)

Acid Rain 1 7-27

Lesson 7

Discussion and results

Extensions

7-28 I Acid Rain

Part Ill: Student material

1. Which dilutions caused the least amount of damage? Compare plants with the control group.

2. Could varying your soil types change your results?

3. Would different seeds act the same as Brassica rapa?

4. How else would you have done this experiment?

1. What are the effects of acid rain on other plants?

2. What would happen if you grew your seeds in an alkaline soil?

3. Would seeds of the Brassica that grew in the lowest pH produce a more resistant plant?

4. Would these resistant plants grow and develop at the same rate as previous generations?

5. Could you change the pH during the growth cycle to improve growth? What would you add?

6. What would happen to fish or insects in an acidic rain?

7. Can you change your pH by adding some soil amendment? If so, what could you add? Experiment further.