Rain and wet weather don’t always mean good news for plants, especially in an area hit by acid rain. Acid rain is caused by the burning of fuels such as oil and coal. This burning releases sulfur dioxide and nitrogen oxide gases, which react with ozone in the atmosphere to form two destructive substances: sulfuric acid and nitric acid. Rain then washes these acids out of the atmosphere and down onto Earth, harming forests and lakes. How exactly does acid rain affect plant growth? Be your own weather-person and find out!
*CAUTION: Don’t try this at home! Ask your science teacher to help you at school.
What you’ll need:
- seeds (bean seeds work well)
- two plastic pots
- potting soil
- light source
- plastic wrap
- distilled water
- 2-liter plastic soda bottle
- medicine dropper
- nitric or sulfuric acid (ask your science teacher to help you get this)
- pH paper (again, ask your science teacher to help you get this)
- two spray bottles
What to do:
1. Plant the seeds in pots with moist potting soil, water them and place them in bright light.
2. When the bean seedlings have emerged with their first pair of full-grown leaves, label one plant container “acid” and the other “control.”
3. Use a separate piece of plastic wrap to cover each half of the soil surface in each pot. The stem should poke through between the two pieces of plastic.
4. Pour one liter of distilled water into a clean 2-liter soda bottle.
5. Ask your science teacher to help you add a drop of nitric acid or sulfuric acid to the distilled water. Swirl the water in the bottle to mix.
6. Test the water pH using pH paper. If the pH is above 3, add more acid. If it is below 3, add more distilled water. Test the water pH until it is about 3. Then pour it into a spray bottle.
7. Place the control plant into a sink and mist the leaves with a spray bottle full of pure distilled water. Let the leaves dry, then bring the control plant back to its growing location.
8. Place the acid plant in a sink, and mist the leaves with the spray bottle filled with pH 3 solution. Let the leaves dry, then bring the acid plant back to its growing location.
9. Observe any differences in growth and leaf color between the acid and control plant.
The plant sprayed with the pH3 solution will be badly damaged. Its leaves will turn brown or yellow.
Why this happens:
Rain is normally somewhat acidic because carbon dioxide gas will dissolve in it to make carbonic acid. As a result, normal rainwater has a pH of 5.6. Fossil fuels like coal or gasoline change the pH, however. When these fuels are burned, they release sulfur dioxide and nitrogen oxide gases into the air. These gases react with sunlight, ozone, and water vapor to form nitric and sulfuric acids.
Rain that is tainted by these acids has a pH that is much less than 5.6. When the pH is below 5.6, it is called acid rain, and this low pH can harm plants. For a further investigation, find out if you have acid rain in your area. Place plastic containers outside to collect rainwater, then measure the pH of this water with your pH paper.