In this experiment, you’ll be testing the affects of acidic water on plant growth and development. By the end of the experiment, you’ll understand the impact of acid rain on the ecosystem.

Introduction

Research Question: What is the relationship between acid rain and plant growth?
Age: 5th grade and up
Safety concerns: None
Time: About 1 week depending on how long it takes the seeds to sprout
Independent variable: Water pH
Dependent variable: Plant height
Controlled variables: Type of plant, amount of water, growing conditions

Picture Los Angeles, California. Although you might be picturing glamourous beaches and movie stars, there’s another side to Los Angeles too. If you catch the city in the morning rush hour, you’ll see a thick layer of what looks like fog. However, much more dangerous than fog, this visible pollution is filled with chemicals like sulfur dioxide caused by the combustion of fossil fuels.

Pollution capable of forming acid rain covers Los Angeles
smog

Sulfur dioxide combines with water in the air, forming sulfuric acid. In the clouds, sulfuric acid dissolves into precipitation and returns to the Earth as acid rain, eating away at buildings, plants and animals.

Acidity is measured on the pH scale. Acids have a pH from 1-7, and bases have a pH from 7-14. Acid rain is precipitation with a pH less than 5.6, usually around 4.2. Today, you’ll be investigating how acid rain affects plant growth.

Materials

  • 6 bean seeds
  • 2 small planting pots (about 4” in diameter)
  • Potting soil to fill the pots
  • 2 plastic bags
  • A warm place to store your plants in the sun
  • Two rubber bands
  • Ruler
  • White vinegar
  • pH strips
  • Water
  • Container to mix the vinegar and water in
  • A data table for both normal and acidic water like this:

Day pH Height Observations
0
1
2
3
4
5
6
7

Steps

1. First, create an acidic solution for the plants. Take 1 cup of tap water and add a few drops vinegar and swirl it around to mix. Use a pH strip to test the solution. Continue adding vinegar until the solution is at pH 4. This will be your ‘acid rain’. Write the initial pH down in your data table for day 0.

2. Also record the pH of the plain tap water you intend to use.

3. Now, it’s time to start our seeds. Fill each pot with potting soil. Next, using one finger, create three small holes about 1” deep. Place one seed in each hole. Lightly cover the seeds with soil.

4. Label each pot ‘acid rain’ or ‘water.’

5. Add about 1/4 cup of either the acid rain solution or water to each pot.

6. Cover your plants with the plastic bags and secure with the rubber bands around the outside of the pots. This will create a moist, humid environment for your plants to sprout. Place your pots in a warm area with direct sunlight.

7. Each day, record the pH of the solution before you apply it to the plant and add 1/8th cup of water or acid rain. Record any observations.

8. When the plants have sprouted, which usually occurs in a few days, remove the plastic. Also, make sure each pot only has one plant growing in it. If more than one seed sprouted, remove all of them except the one you are measuring.

Within a few days, small plants with two leaves should have sprouted
sprouted plants

9. Each day, add 1/4 cup of the acid rain solution or water to the plants after they have sprouted. Take the pH of the solution before you apply it, and record it, along with the height of your plant, for the rest of the week.

Troubleshooting

If your plants aren’t sprouting, make sure they are somewhere warm. Heat mats can easily solve this problem and can be bought at garden supply stores. You may need more or less water to keep your plants moist, just make sure you add the same amount of water to both plants. If your seeds in plain water sprout, but not your seeds in acid rain, consider this part of your data.

Discussion Questions

What differences did you notice between the plant receiving water and the plant receiving acid rain?

Why do you think an acidic solution is bad for plants?

How It Works

Plants are autotrophs, meaning they make their own food. To do this, plants contain a special chemical inside their cells called chlorophyll. Chlorophyll captures light energy from the sun which the plant can use to make food during photosynthesis. The plant will then use the food to grow and make new structures.

Acid interferes with chlorophyll production. Acid rain causes chlorophyll to be converted to a form that isn’t usable. This means that the plant can no longer do photosynthesis, so new structures can’t be made and is why you probably saw far less growth in the plant treated with acid rain.