Water Testing: What Makes Water Good?

Transcription

1 Water Testing: What Makes Water Good? We have been learning about the chemical makeup of water and how to test water for hardness, ph, copper and chlorine. We have read and discussed what it means if the water is hard or soft, or if the ph is neutral, alkaline or acidic. Now we are going to consider the question: What makes water good? In this investigation, your team will conduct and compare several tests on different water samples to try to determine what makes each water sample good and which one is the best for you to drink, to wash with, etc. Use your data to draw your conclusions. 1 of 13

2 Suggested Grade Span 3 5 Task We have been learning about the chemical makeup of water and how to test water for hardness, ph, copper and chlorine. We have read and discussed what it means if the water is hard or soft, or if the ph is neutral, alkaline or acidic. Now we are going to consider the question: What makes water good? In this investigation, your team will conduct and compare several tests on different water samples to try to determine what makes each water sample good and which one is the best for you to drink, to wash with, etc. Use your data to draw your conclusions. Big Ideas and Unifying Concepts Cause and effect Change and constancy Interdependence Systems Physical Science Concept Properties of matter Earth and Space Science Concept Earth structure and system Science in Personal and Societal Perspectives Concept Personal health Mathematics Concepts Comparison of attributes and effects Data collection, organization and analysis 2 of 13

3 Time Required for the Task Approximately five 45-minute class sessions, including four lead-up activities to learn how to do each water test. Context This inquiry was part of our unit on water. To introduce the science concepts and skills in testing water for hardness, ph, copper and chlorine, students participated in four guided activities that explored the quality of water. Each day, we completed one test on the water in our classroom using Hach Water Quality Test Strips. Students had a one- to two-page overview of each test and directions to follow using the test strips. After each test, we recorded the results and discussed what the data meant. For example, because most water pipes are made of copper, you would not want a ph to be acidic (below a ph of 7) since copper would dissolve from the pipes and go into the water. Pipes that dissolve would also begin to leak over time. Each activity explained a little about one characteristic of water and guided students in how to conduct the tests. As the students worked, they built their understanding of the nature of water as a solvent and improved their ability to apply some of the skills of scientific investigation. Students were then encouraged to compare different water samples in order to answer the question: What makes water good? What the Task Accomplishes This task provides information to the teacher about whether students are building an understanding of the characteristics of water and can use scientific reasoning to evaluate the quality of water for particular uses (for example, if water is hard, soap does not work well; however, it is not bad for drinking). This task demonstrates how well students can use scientific tools to collect data and show evidence of conceptual understanding in how they interpret data. Students have the opportunity to communicate their results to the class and learn from what other students have investigated. How the Student Will Investigate After the guided investigations with the whole class, teams of two to four students then repeated the tests with the classroom water and then chose a second water sample from several choices of bottled water to conduct the four tests on as well. Finally, students interpreted their data and discussed conclusions based on the data collected. Each group shared their investigation and results with the class. Class sharing is a way that teachers can check understanding, make connections to prior knowledge, and extend thinking to the next lessons in the unit and/or introduce new science vocabulary. 3 of 13

4 Note: For teachers who have little background in conducting these tests, the Hach Water Quality Test Strips and teaching materials are user friendly and written for easy conceptual understanding, even for third graders. Interdisciplinary Links and Extensions Science Students may want to conduct further investigations with other water samples, such as the water they have at home. Concepts learned in these activities can build a foundation for more in-depth investigations with solvents and solutions. Teaching Tips and Guiding Questions Guiding questions to ask students before, during and after investigations might include: What makes water hard or soft? What does that mean? How does water become hard? (Water, a solvent, picks up impurities easily. When water flows over rocks, it can pick up calcium and/or magnesium salts from limestone or other rocks. These salts dissolve in the water, making it hard.) Why doesn t soap work well in hard water? (Soaps contain long chain-like molecules that have two distinct ends. One end interacts with water and the other end interacts with oil and grease. If there is too much magnesium or calcium in the water, the end of the soap molecule that is supposed to react with the dirt and oil ends up reacting instead with the magnesium or calcium. This makes soap scum bunched-up soap molecules.) How can hard water hurt pipes? (It can accumulate and clog the pipes.) What is ph? What does it mean to be neutral? acidic? alkaline? (ph is a way to measure how acidic or alkaline a solution is. The ph scale goes from 0 to 14. If there is an equal number of hydroxide and hydroxyl ions, the solution is neutral and has a ph of 7. Because a water molecule is made of one of each ion, pure water is neutral. If the solution is less than 7, it is acidic; greater than 7, it is a base, or alkaline.) Why do some water suppliers (like the town) add alkaline substances to the water to raise the ph? (To slow or prevent acidic water from eating the pipes from the inside.) Why are there sometimes blue-green stains in your bathtub? (Copper has dissolved in the water.) What do your results tell you? What did you learn from your results? What conclusions can you make based on your results? What new questions do you have about water? Have you learned anything that surprised you? 4 of 13

5 Concepts to be Assessed (Unifying concepts/big ideas and science concepts to be assessed using the Science Exemplars Rubric under the criterion: Science Concepts and Related Content) Physical Science Properties of Matter: Students observe and compare physical properties of matter to make predictions and classify materials. Scientific Method: Students observe and explain reactions with some justification, using data and prior knowledge, when variables are controlled (cause and effect). Students determine the patterns and/or which kinds of change are happening by making observations and measurements over time (change and constancy). Earth and Space Science Earth Structure and System: Students observe that water is a solvent. As it passes through the water cycle, it dissolves minerals. Science in Personal and Societal Perspectives Personal Health: Students understand that nutritional balance has a direct effect on growth, development and personal well-being, and that the water you drink and cook your food with can affect your health. Mathematics: Students collect, organize and analyze data appropriately and compare attributes or effects. Skills to be Developed (Science process skills to be assessed using the Science Exemplars Rubric under the criteria: Scientific Procedures and Reasoning Strategies, and Scientific Communication Using Data) Scientific Method: Raising questions, hypothesizing, observing, predicting, testing, measuring ph, manipulating tools, collecting/recording data, interpreting data, drawing conclusions and challenging misconceptions. Other Science Standards and Concepts Addressed Scientific Method: Students hypothesize, observe, predict, investigate and explain phenomena. Scientific Theory: Students use evidence to construct an explanation based upon their observations and the concepts that have been learned. Students modify explanations when new observations are made. Physical Science Properties of Matter: Students describe and sort objects and materials according to observations of similarities and differences of physical properties. Students understand that properties and changes of properties in matter (ph) can cause changes in ecosystems. 5 of 13

6 Earth and Space Science Earth Structure and System: Students observe that water is a solvent. As it passes through the water cycle, it dissolves minerals and gases and carries them to the oceans. Science in Personal and Societal Perspectives Personal Health: Students understand that selection of foods and eating patterns determine nutritional balance, and that nutritional balance has a direct effect on growth, development and personal well-being. Suggested Materials Items to have available during investigations include different brands of bottled water, tap water, measuring cups, small paper cups and Hach water test strips. Additional investigations might also use different kinds of dish soap and distilled water. Possible Solutions In this investigation, students need to list materials used, conduct the four tests and record their data for two water samples (tap water and bottled water). Then, students should be able to write an explanation for which water sample they think is better, based on the data they collected. Task-Specific Assessment Notes Novice This student completes the testing but fails to list the materials used. Only one result is discussed, but four tests are conducted. The numbers for hardness are questionable. There is little evidence of conceptual understanding. Apprentice This student completes the testing and lists the materials used. Results reflect information read in class rather than an analysis of the test results or comparisons between the two samples. There is some evidence of conceptual understanding. Practitioner This student includes a list of materials used and collects all of the data from the four tests. The discussion of results compares each quality tested and demonstrates conceptual understanding that builds on prior knowledge and experience. Expert This solution includes a list of materials and data from all tests conducted. Because the students are curious, they also test seltzer extending thinking beyond earlier investigations. The discussion of results include information learned in class, information learned through the testing, and comparisons of the data. There is clear evidence of conceptual understanding. 6 of 13

7 Novice 7 of 13

8 Apprentice 8 of 13

9 Apprentice 9 of 13

10 Practitioner 10 of 13

11 Practitioner 11 of 13

12 Expert 12 of 13

13 Expert 13 of 13