Measuring pH of Direct and Throughfall Rain

A Rising Tide Project for Grades 11 and 12

Classroom Activity
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Classroom Activities
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Glossary

Main l Classroom Activity l Objectives l Standards Addressed l Background l Methods/Teacher Guide l Rubric l Resources

Identify the problem:  The purpose of this laboratory experience is to investigate the difference between the acidity of rain that falls directly on the ground to the acidity of rain that falls through tree branches.   Will there be a difference?  Why or why not? 

Gather information:  Research acid rain (its causes and composition), the pH scale, acids and bases, and all key terms provided with this lab. 

Form an hypothesis: Begin by writing the first rough draft of the laboratory report. Label the first section of this report ‘Introduction’. 

1. In the first paragraph(s) describe the problem that is being investigated in this activity. 
2. In the next paragraph(s) describe/explain the research information that you have gathered.  Define the terms ‘acid rain’ and how it is created by human activities.  Explain the difference between ‘direct rain’ and ‘throughfall rain’.  Refer to the ‘Key Terms’ list for terminology that should be used in your writing. 
3. In the next paragraph(s), state your own hypothesis.  Explain, in detail, the reasoning for your prediction. 

 Design the experiment:  The following list of materials and procedures are given as a guideline for you to use.  You will need to adjust both the materials list and procedures as you design this experiment to accurately test your own specific hypothesis. 

1. Label the second section of your laboratory report ‘Materials’. 
2. List all laboratory equipment and materials in a column (or two). 

EXAMPLE:

      Materials

            14 ring stands with bases                         14 - 2L or 16 ounce clean plastic bottles
            Scissors                                                            Masking tape
            Marker                                                          14 sandwich bags
            pH meter (with accessories)                   calculator

3. Label the third section of the report ‘Procedures’.

EXAMPLE:

      Procedures

1.      Use scissors to cut off the top 3 inches of each plastic bottle.

2.      Use masking tape to secure one bottle to each ring stand.  Make sure the bottoms are securely seated on the base of the ring stands.  

3.      Label the masking tape around each bottle as follows: 

a.     Label the seven ‘open field’ bottles:  OF - #1, OF - #2, OF - #3, OF - #4, OF - #5, OF - #6, and OF - #7. 

b.     Label the seven ‘throughfall’ bottles:  TF - #1, TF - #2, TF - #3, TF - #4, TF - #5, TF - #6, and TF - #7. 

4.      Place the bottles outside in the rain. 

a.      Place the ‘open field’ bottles in an area on the ground that has no overhead vegetation. 

b.     Place the ‘throughfall’ bottles in an area on the ground underneath tree branches.   Do not place the bottles too close to the trunk – this may prevent rain from being able to fall into the bottle.   Place bottle approximately 2 feet away from the trunk. 

5.      After rainfall:

a.     Cover each bottle with a sandwich baggie.  This will help prevent contamination of the water sample while moving the ring stands from outside into the classroom. 

b.     Calibrate the pH meters according to the instructions provided.

6.       Collect, record, and calculate information: 

a.     Each student should measure the pH of each water sample and record the information. 

b.     Each student will construct two data tables.  Each data table must contain proper labels and titles.  The data tables should be on separate pieces of paper and attached to the back of the report. 

c.     Attachment A: Average pH of Direct Rain

d.     Attachment B: Average pH of Throughfall Rain

Attachment A: Average pH of Direct Rain

The data table: 

3 columns: 

·        ‘bottle number’;

·         ‘pH measurement’

·        ‘average pH’     

7 rows:  one for each bottle

·        List a bottle number for each bottle. 

·        For each bottle, list all measurements made by each student under the column ‘pH measurement’. 

·        Calculate the average for all pH measurements made on the Direct Rain samples and record this under ‘average pH’. 

The calculations: 

Below the data table, state the range for Direct Rain pH levels.

Example:  Range = pH 4.81 to pH 6.19

Below the range, show all calculations for the mean of the data.

Example:             Mean

                        Add all pH averages, divide by 7

                        Add:  6.08, 4.81, 4.84, 4.98, 6.19, 5.08,  5.42=                                                                         37.4

                        Divide by 7 (number of bottles):  37.4 / 7  =                                                                    pH 5.34

Attachment B, Average pH of Throughfall Rain

The data table: 

3 columns: 

·        ‘bottle number’;

·         ‘pH measurement’

·        ‘average pH’     

7 rows:  one for each bottle

·        List a bottle number for each bottle. 

·        For each bottle, list all measurements made by each student under the column ‘pH measurement’. 

·        Calculate the average for all pH measurements made on the Throughfall Rain samples and record this under ‘average pH’. 

The calculations: 

Below the data table, state the range for Throughfall Rain pH levels.

Example:  Range = pH 4.81 to pH 6.19

Below the range, show all calculations for the mean of the data.

Example:             Mean

                        Add all pH averages, then divide by 7

                        Add:  4.69, 5.79, 4.60, 5.90, 4.78, 5.93, 6.22  =                                                                     37.91

                        Divide by 7 (number of bottles):  37.91 / 7  =                                                                   pH 5.42 

Report the results.  The fourth section of the report is labeled ‘Results’.  In complete sentences only report the calculated mean for both the direct and throughfall rain.  The last sentence should read, “See Attachments A and B.” 

Form a conclusion:  The fifth section of the report is labeled ‘Conclusion’. 

1.      In the first paragraph(s) restate your hypothesis.  State whether or not it is a valid or null hypothesis.  Use the measured and calculated pH values to explain why it is either valid or null. 

2. In the next paragraph(s) explain what you learned from this experiment.  Try to write answers to these questions: 

Q:  Did the rain that fell directly on the ground have the same pH as that which fell on the trees? 

Q:  Is there any evidence that deposition or leeching caused a change in pH?

3. In the next paragraph(s) explain the next step a scientist could take to measure the effects of acid rain on trees.  Here are a few ideas to write about:

Q:  What if acid rain causes other elements to leach out of leaves or stems?  Are these other elements necessary for plant growth? 

Q:  What if acid rain damages leaves because it goes into a chemical reaction when mixing with organic deposition?  Are leaves necessary for plant growth?

Q:  What if acid rain damages only leaves that do not have organic deposition?  Is it more beneficial for trees to have a coat of organic deposition or be clean? 

 Evaluation:  Write an edited copy of the laboratory report using a student copy of the rubric.  Submit the report to your teacher for grading with an unmarked, clean copy of the rubric attached to the top.