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1 W A T E R Q U A L I T Y Acid Rain Riddle techsupp@pasco.com

2 ACID RAIN RIDDLE WATER QUALITY Grades 5 8 Grade Levels Time Required One 50-minute session National Science Standards Water Quality UCPs 1-5 Content Standard A A-1:1-6 A-2:1-6 Content Standard B B-1:1 B-1:3 B-2:4 B-2:5 B-3:1 B-3:3 Content Standard C C-4:1 C-5:5 Content Standard D D-2:1 Content Standard E E-1:1-5 E-2:1-4 Content Standard F F-2:3 F-3:1-3 F-4:1-3 F-5:2 F-6:1-5 Content Standard G G-1:3 G-2:1-3 G-3:2-3 Please see the Standards Section for additional Standards achieved, specifically the: National Science Teaching Standards NCTM Mathematics Standards National Education Technology Standards Information Literacy Standards The Standards achieved are followed by a PASCO Coding Legend for each set of Standards. Overview Students will observe the effect of acid rain on water from three water sources, and determine that the water from a clear mountain lake is most affected by the addition of acid rain. Moreover, students will learn that there are natural processes in some bodies of water that provide natural buffering to acid rain. Learning Goals Students will: Determine the ph of three water samples, representing water from a clear mountain lake, a pond, and the ocean. Add a small amount of acid to the first sample, and measure the ph. Repeat the procedure for each of the samples. Determine that the sample from the ocean recovers from the addition of the acid because of the natural buffering processes that occur in the water. Relate ph to level of acidity. Recognize that acid rain can change the ph level of a natural water body. 77 Teacher Information Pages

3 WATER QUALITY Background Acid rain? What is it? First of all, it is handy to know a little bit about the terms acid, base, and neutral. So here is an overview of the measurement of acids and bases called ph. A little bit about ph ph is a measure of the number of hydrogen ions present in a substance. The ph scale goes from zero (corresponding to a very acidic substance) to 14 (the strongest base measurement). A substance which is neutral (neither acidic nor basic) has a ph of 7. Pure water is neutral, and therefore, has a ph of 7. From a practical standpoint, the neutral zone is considered to be the range between and Anything with a ph below 7 is acidic; above 7 means that the substance is basic. A CID RAIN RIDDLE acid rain alkaline base basic buffer neutral snert Vocabulary See Glossary for vocabulary definitions Materials Acids: Have free hydrogen ions; Taste sour; Turn litmus paper red; Bases: Have a ph above 7; Absorb hydrogen ions; Taste bitter; Feel slippery, like soap; Turn litmus paper blue. PASCO Equipment for Acid Rain Riddle Activity PASPORT USB Link or Xplorer PASPORT ph Sensor DataStudio software General Equipment Computer with USB port scissors three water samples representing: -high mountain streams -valley pond water -ocean water (see recipes if not locally available) white vinegar paper towels DataStudio Workbook: Acid Rain Riddle Team Response Sheet: Acid Rain Riddle Student Information Sheet: Acid Rain Riddle Teacher Information Pages 78

4 ACID RAIN RIDDLE WATER QUALITY Teacher Tip Classrooms with limited computer resources: If student groups do not have access to a computer, use the Xplorer to collect the data. Set the Xplorer to collect single data points, and record the data point when the reading stabilizes. Provide students with a paper copy of the DataStudio Workbook to guide them during the activity. Now that we know a little about ph: What is acid rain? Rain is naturally slightly acidic because carbon dioxide in the atmosphere dissolves in rainwater and forms a weak acid. This slightly acidic rain is actually beneficial because it helps dissolve minerals in the soil that plants and animals need. However, when rain s ph falls below 5.5, it is called acid rain and it can be harmful to the environment. Acid rain can adversely affect aquatic wildlife, forests, and manmade structures such as monuments and statues. What causes acid rain? Acid rain is formed when moisture in the atmosphere reacts with substances such as sulphur dioxide and nitrogen oxide, resulting in precipitation that is acidic. (Just for fun: Do you know what acidic snow is called? Answer: Snert). 79 Teacher Information Pages

5 WATER QUALITY A CID RAIN RIDDLE What level of ph is safe? Okay, this concept of safe is going to keep coming up. The answer is: it depends on the use of the water. Something that is safe for one use may not be safe for another. For example, some types of plants need acid to do well. If you have gardenias and azaleas, there is special fertilizer that is acidic, and the plants grow well and will produce beautiful flowers when given acid in their water. On the other hand, insects (which are food for fish in lakes) will not survive in water that is acidic. Table 1 shows the effects of ph levels on aquatic organisms. Another thing to keep in mind is that some rocks contain heavy metals, which can be toxic to aquatic organisms. And rocks and minerals are more easily dissolved in an acidic environment. This means that if a lake becomes acidic, the creatures living in the lake may not survive. But even if they survive, the acid may cause heavy metals from the rocks around the lake to dissolve, which then would cause additional problems for the creatures. So maybe they could survive the change in ph, but the addition of heavy metals might create problems. ph Level Table 1: Effects of too much acid in the water <6.0 Basic forms of food die off. (Mayflies and stoneflies are important food sources for fish, and the flies cannot survive at this ph level). <5.5 Fish cannot reproduce. Young fish have difficulty surviving. Lack of available nutrients result in deformed adult fish. Fish die of suffocation. <5.0 Fish population dies off. Teacher Tip Recipe for Pond Water If you do not have a source for pond water, you can easily make some. Mix: 1 L deionized water 60 mg NaCl 6 g ground oyster shells (from your local garden supply store) Filter this mixture. The resulting conductivity will be similar to a typical valley pond ( µS/cm). Teacher Tip Recipe for Mountain Lake or Stream Water If you do not have a source for high mountain water, you can easily make some. Mix: 20 ml of the artificial pond water (from the recipe above) 250 ml deionized water or filtered tap water. What things can affect the ph of a body of water? Glad you asked. Things that affect the ph level of water fall into 2 categories: (1) natural, and (2) man-caused. Teacher Information Pages 80

6 ACID RAIN RIDDLE WATER QUALITY Teacher Tip Recipes for Ocean Water If you do not have a source for ocean water, you can easily make some g Instant Ocean (sold at most stores that sell fish and aquarium supplies) 1 L deionized water or filtered tap water. You will have a solution that is very close in composition to ocean water Alternatively mix: 35 g table salt (NaCl) 6 g ground oyster shells 1 L deionized or filtered tap water Filter this mixture You will have a buffered solution that has a salinity close to that of ocean water. Of course, the real thing is always best! The naturally occurring things include: Types of rocks and soils near the water body. Some types of rocks, such as limestone, contain chemicals that act as a buffer. A buffer is a solution to which an acid can be added without changing the ph very much. A buffer essentially absorbs the excess H + ions and protects the body of water from fluctuations in ph. So, water in areas that have a lot of limestone rock is naturally buffered and protected from changes in ph when acid is added. If, on the other hand, the rocks near the water body do not dissolve easily (such as granite), the natural buffering does not occur. The ph of the water would be more influenced by outside factors. If an acid were added to water in this region, the ph would likely become more acidic. Biological activities of plants and animals in the water. When plants and animals respire, carbon dioxide is produced, and carbolic acid is produced when carbon dioxide is dissolved in water. This causes the water to become acidic (the ph increases). So think of what this means plants and animals actually increase the acid level of the water. Man influences the ph of water bodies: directly by discharging waste in or near the body of water, and indirectly by influencing the ph of rain, which may fall into the body of water (acid rain). What is alkalinity? Alkalinity is the capability of water to neutralize acid. Some chemicals that are dissolved in water, such as calcium carbonate, increase the alkalinity of the water. Calcium carbonate is found in limestone. Water that has some alkalinity does not change its ph when acid is added through acid rain because the substances that produce the alkalinity act as a buffer and neutralize the acid. Water that has a high amount of alkalinity has a basic ph. 81 Teacher Information Pages

7 WATER QUALITY Engage Students will be asked to predict which will be more affected by acid rain: mountain stream water, pond water, or ocean water. They will be challenged to test and find out the answer. Explore The DataStudio Workbook has instructions for equipment setup. A CID RAIN RIDDLE Teacher Tip Recipe for Acid Rain You can simulate acid rain by mixing 1 part white table vinegar with 9 parts water. This mixture has a ph of about 3, which is about 10 times more acidic than the most acid of acid rain. If you choose to do a 1:99 dilution, the resulting acidity will be closer to actual acid rain, but you will have to add 10 times as much to your water samples to see the desired effect. The Acid Rain Student Instruction Sheet prompts students to assume a team role and provides students with step-bystep instructions for this activity. The Acid Rain Team Response Sheet will prompt students to analyze the results of this activity and provide you with assessment opportunities. The Acid Rain Riddle Information Sheet has information that students will need as they answer questions on the Team Response Sheet. Resources Go to our Resources Page on the Web to find links to related sites: Teacher Information Pages 82

8 ACID RAIN RIDDLE WATER QUALITY Assessment Formative assessment As students are working in their groups, circulate to determine if: Individual students are participating in the activity. Individual students are completing the responsibilities of the roles to which they have been assigned. Team members are discussing the worksheet and contributing to the formulation of answers. And pose questions such as: Which water is the most acidic? How do you know? Is there a difference in the sources of the water samples? What represents the acid rain? Do you think that any of the samples are pond water? Why or why not? Summative assessment Do the students understand that some waters are naturally buffered? Can they relate the experiment to real world situations? Are they able to determine which water sample represents the pond water? Extensions Have students design their own experiments to investigate the acid buffering capacity of water sources in your area. Students can do an Internet search on acid rain to find out more about the current global situation concerning acid rain. 83 Teacher Information Pages

9 WATER QUALITY ACID RAIN RIDDLE Acid Rain Riddle- Student Instruction Sheet Team Challenge Which water source is least affected by acid rain: mountain stream, pond, or ocean? Equipment and Materials Equipment Materials Computer with USB Port three water samples: (250 ml each) PASPORT USB Link or Xplorer -mountain stream water PASPORT ph Sensor -valley pond water DataStudio Software -ocean water ml beakers white table vinegar graduated cylinder paper towels beaker for waste water Acid Rain Riddle Student Instruction Sheet wash bottle Acid Rain Riddle Student Information Sheet Acid Rain Riddle Team Response Sheet Safety Precautions Computer Care: Use care when handling liquids near the computer. Follow the teacher s instructions for placement. Place the buffer storage solution for the ph sensor in a secure location. Student Instruction Sheet 84

10 A CID RAIN RIDDLE WATER QUALITY Procedure 1. Set up the equipment as shown in Figure Obtain 250 ml water samples from the three sources provided by the teacher. Label each beaker so that you don t mix up the sources of the sample. ph Sensor beaker with water sample 3. Open the DataStudio file: Acid Rain Riddle Figure 1. Setup for Acid Rain Riddle 4. Follow the directions in the DataStudio workbook. Make sure that you use the same amount of each sample of water and that you add the same amount of acid rain to each. 5. Answer the questions and complete the discussion on the Team Response Sheet. Remember to use the information that you gleaned from the Student Information Sheet. 6. Clean-up: Return all equipment and materials. Dispose of the water samples as directed by your teacher. Don t forget to rinse all of the glassware and the ph Sensor. Be sure you leave your area clean for the next class. 85 Student Instruction Sheet

11 WATER QUALITY ACID RAIN RIDDLE Name Period Team Response Sheet Teacher s Version Roles and Responsibilities Role Description of Responsibility Name of Assigned Team Member Team Leader/ Spokesperson Materials Organizer and Handler Data Recorder Equipment Operator Responsible for making sure the group stays on task and moves efficiently through the assignment; speaks for the group during class summaries. Responsible for getting the necessary equipment and materials for the station; oversees clean-up. Responsible for recording team consensus responses on the Team Response Sheets. Responsible for operating the ph Sensor and computer or Xplorer. Jeff Jonathan Rachel Jacob Predict Record the ph for each of the samples in the spaces provided. Predict what will happen to the ph when acid rain is added to the sample. Type of Water Sample Initial ph What do you think will happen to the ph when acid rain is added Mountain stream 8.3 The ph will go down. Pond 9.1 The ph will decrease a little bit. Ocean 8.4 The ph will go down a whole bunch. Team Response Sheet Teacher s Version 86

12 A CID RAIN RIDDLE WATER QUALITY Record Follow the instructions for adding acid rain to each of the water samples. Record the final ph for each sample. Type of Water Sample Initial ph Final ph Change in ph Mountain stream Pond Ocean Discuss Describe what happened to the ph of each of the samples. Did all of the samples respond in the same manner? Why do you think this happened? When we added the acid rain to the beakers, all of the water samples responded with a decrease in ph. This means that all of the water samples became more acidic. But the mountain stream water had the greatest change. The ph of mountain stream water went from 8.3 to 5.7, a decrease of 3.1. The change in pond water was 1.2 (it went from 8.8 to 7.6). Finally, the ocean water changed only slightly (from 8.2 to 7.8, a difference of 0.4). We talked about why the ocean water was not as impacted by the acid rain as the mountain stream water. One thought that we had was that since the ocean is so large, it wouldn t be impacted as much. But then we talked a little bit more and realized that we had used the same amount of water in our experiment, so that the size of the ocean wouldn t be a part of the effect (This has something to do with variables. We had the same amount of water in each of our samples, and used the same amount of acid rain, so that the only thing that we varied was the water sample itself.). This means that what was in each sample was what caused the differing effect of acid rain. All of the samples were at about the same temperature, so temperature wouldn t be a factor. We think that we need to find out what was in the water samples before we can figure out why there was such a difference in responses to acid rain. We are thinking that there must be something in the ocean water and the pond water that reacts with the acid rain so that the ph doesn t change as much as does the fresh mountain stream water. 87 Team Response Sheet Teacher s Version

13 WATER QUALITY A CID RAIN RIDDLE Name Roles and Responsibilities Period Team Response Sheet Role Description of Responsibility Name of Assigned Team Member Team Leader/ Spokesperson Materials Organizer and Handler Data Recorder Equipment Operator Responsible for making sure the group stays on task and moves efficiently through the assignment, speaks for the group during class summaries. Responsible for getting the necessary equipment and materials for the station. Oversees clean-up. Responsible for recording team consensus responses on the Team response sheets. Responsible for operating the ph Sensor and computer or Xplorer. Predict Record the ph for each of the samples in the spaces provided. Predict what will happen to the ph when acid rain is added to the sample. Type of Water Sample Initial ph What do you think will happen to the ph when acid rain is added Mountain stream Pond Ocean Team Response Sheet 88

14 A CID RAIN RIDDLE WATER QUALITY Record Follow the instructions for adding acid rain to each of the water samples. Record the final ph for each sample. Type of Water Sample Initial ph Final ph Change in ph Mountain stream Pond Ocean Discuss Describe what happened to the ph of each of the samples. Did all of the samples respond in the same manner? Why do you think this happened? 89 Team Response Sheet

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