Name: ______Class: ______Date: ______

Visualizing Differences in Rainwater pH Levels

Introduction

The pH scale is used to determine if a substance is an acid, base, or neutral. This is an important chemical analysis tool of environmental science, as most living things have a specific range of pH levels they can thrive in. While the scale is easy to understand, the actual differences between the pH levels is not.

1.Given the examples shown above, what pH do you think would be ideal for a saltwater aquarium containing species of fish found in a coral reef? Justify your answer.

2.What pH do you think would be ideal for the soil that most trees grow in? Justify your answer.

3.What is the normal pH of pure rainwater? Would you consider this to be a strong or weak acid or base?

4.Acid precipitation occurs when rain or snow falls that has a pH lower than is expected from pure rain. What kinds of effects would you expect to see on plant life from acid rain? On trees and other plants?

Acid Precipitation in the United States

This data is taken from measurements made by the National Acid Deposition Program in 1993. The darker areas indicate lower recorded rainfall pH levels.

5.What region of the country seems to have the biggest problem with acid precipitation?

6.What is the lowest tested pH found anywhere on this map?

7.What is the tested pH level of the rainfallin your area, based on this data?

Visually Comparing pH Levels

This lab will have you take several simulated acid rain samples and determine how much of each is required to completely neutralize a given base.

Hypothesis:

  1. How much stronger of an acid do you expect the acid rain with a pH of 4.2 will be compared to normal rain with a pH of 5.6? Write a specific quantitative prediction below.

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Materials:

  • Test tube
  • Eight simulated rain samples (pH 5.6-4.2)
  • 0.01M Sodium hydroxide (NaOH)
/
  • Dropper bottle of phenolphthalein
  • Safety goggles
  • Graduated cylinder

Procedure

  1. Label eight of the test tubes with the pH of the different rain samples. There should be eight samples ranging from a pH of 5.6 to 4.2.
  1. Put 5mL of NaOH into the unlabeled test tube.
  1. Add 1 drop of the phenolphthalein solution to the test tube. The solution should change color.
  1. Add one drop of the pH 5.6 rainwater sample to the test tube. Stir the test tube by lightly tapping it with your finger.
  1. Continue to add drops of the rainwater sample to the test tube until the color disappears. Record the total drops of acid added to the solution in your data table.
  1. Pour out the neutralized solution down the sink and rinse with water.
  1. Repeat steps #2-6 for the other rainwater samples.

Data

Table 1: Drops of Rainwater Sample Needed to Neutralize NaOH

pH of Rainwater Sample / Number of Drops to Neutralize NaOH

Table 2: Drops of Rainwater Sample Needed to Neutralize NaOH (Class Data)

Normal Rain pH = 5.6 / Acid Rain
pH = 5.4 / Acid Rain
pH = 5.2 / Acid Rain
pH = 5.0 / Acid Rain
pH = 4.8 / Acid Rain
pH = 4.6 / Acid Rain
pH = 4.4 / Acid Rain
pH = 4.2
  1. In this data set, what is the independent variable that you are controlling?
  1. In this data set, what is the dependent variable that you are measuring?
  1. Create a bar graphbased on your collected data. Remember, the independent variable should be on the x-axis and the dependent variable should be on the y-axis.

  1. Based on the graph you completed above, do the results support your hypothesis, or should it be rejected? Explain.
  1. Why is abar graphthe best option in displaying data like this?

Conclusion

  1. On the surface, a difference between a pH of 4.2 and 5.4 does not seem very significant. Explain exactly how much stronger of an acid the 4.2 pH rainwater is compared with the 5.4pH rainwater.
  1. A common source of acid rain is air pollution that contains sulfur. This creates sulfuric acid when it mixes with water vapor in the air. Sulfur air pollution is easy to identify because it has a rotten-egg odor. What are some sources of sulfur air pollution you have encountered?
  1. Why does the Eastern mid-Atlantic region of the United States have the biggest problem with acid precipitation?
  1. Go to the National Acid Deposition Program website and look at the current animated maps of sulfate and nitrate ion soil concentration in soil. How has the map changed since the 1980s? How do you account for this change?

SO4 (sulfate) concentration animated map: nadp.sws.uiuc.edu/data/amaps/so4/amaps.html

NO3 (nitrate) concentration animated map: nadp.sws.uiuc.edu/data/amaps/no3/amaps.html

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