CABBAGE COLORS & ACID RAIN: Connecting ph to the Growing Problem of Acid Rain

Transcription

1 elibrary Standards-Based Learning Activity CABBAGE COLORS & ACID RAIN: Connecting ph to the Growing Problem of Acid Rain Teacher Procedures APPROPRIATE FOR: Chemistry/Environmental Science, Grades 9-12 TIMELINE: Two class periods SCIENCE STANDARDS ADDRESSED THROUGH THIS LESSON NSES CONTENT STANDARD B: As a result of their activities in grades 9-12, all students should develop an understanding of: Chemical reactions may release or consume energy. Some reactions such as the burning of fossil fuels release large amounts of energy by losing heat and by emitting light. Light can initiate many chemical reactions such as photosynthesis and the evolution of urban smog A large number of important reactions involve the transfer of either electrons (oxidation/reduction reactions) or hydrogen ions (acid/base reactions) between reacting ions, molecules, or atoms. In other reactions, chemical bonds are broken by heat or light to form very reactive radicals with electrons ready to form new bonds. Radical reactions control many processes such as the presence of ozone and greenhouse gases in the atmosphere, burning and processing of fossil fuels, the formation of polymers, and explosions. CONTENT STANDARD C: As a result of their activities in grades 9-12, all students should develop understanding of: As matter and energy flows through different levels of organization of living systems-- cells, organs, organisms, communities--and between living systems and the physical environment, chemical elements are recombined in different ways. Each recombination results in storage and dissipation of energy into the environment as heat. Matter and energy are conserved in each change CONTENT STANDARD D: As a result of their activities in grades 9-12, all students should develop an understanding of: The earth is a system containing essentially a fixed amount of each stable chemical atom or element. Each element can exist in several different chemical reservoirs. Each element on earth moves among reservoirs in the solid earth, oceans, atmosphere, and organisms as part of geochemical cycles. (source: LEARNING EXPECTATIONS/OBJECTIVES Students will develop their understanding of acids, bases and the ph scale, and apply this knowledge to a study of acid rain. Students will use elibrary to research the causal relationship between industry and acid rain. Students will use elibrary to explore possible solutions to reducing the amount of emissions that promote acid rain.

2 MATERIALS A long glass rod open at both ends Rubber Stoppers for each end of the glass rod HCL and NaOH solution: O.1M. (If you wish to use household products, use vinegar for the acid and window cleaner for the base.) Juice from boiled cabbage, obtained by boiling the cabbage for one hour, then straining and storing the liquid Copies of the activity sheet ACTIVITY PROCESS: DIRECTIONS TO THE TEACHER Description of Activity Students will make their own ph scale using cabbage juice. The scale is straightforward. If a glass tube is filled with cabbage juice, adding HCL to one end and NaOH to the other will cause a progression of colors to appear ranging from red to green. After making their ph scales, students will reinforce their understanding of the acid and base concepts using the attached activity sheet and elibrary. Finally, students will apply their understanding of the cabbage juice scale in order to study and understand acid rain and its connection with the burning of fossil fuels for energy production, transportation, homes, and manufacturing both in the U.S. and the world. Background Information Plant pigments in the plastids of cabbage react with the OH- and H+ ions of the acidic and basic solutions. The pigment anthocyanin displays different colors depending on the amount of hydroxyl groups that attach. At a low ph of 2, reds and oranges can be observed. At a neutral ph of 7, a purple color is observed. And at a ph of 12 blue and yellow superimpose to display green. The following activity is best used to reinforce students understanding of ph. Students should already have a loose understanding of ions and atomic structure. Students should also be familiar with basic chemical equations and the concepts of physical and chemical change. Students do not need any prior exposure to the science behind acid rain. Section II of the activity sheet, entitled Global Connection, will help students understand the relationship of acids and bases to modern-day manufacturing. OUTLINE OF THE PROCEDURE -- DAY 0 -- Homework Orientation Provide a copy of the activity sheet. Encourage students to read through the procedure and questions at home (or even in class), thereby making the day two research an easier and more natural process. OUTLINE OF THE PROCEDURE -- DAY 1 The following exercise should be discovery-based so only a brief introduction is necessary. Focus primarily on the procedure and proper lab safety. Students in groups of 2-3 (or the teacher as a demonstration) will perform these steps to create a ph scale: 1. Stopper one end of the tube and fill four inches from the top with cabbage juice. 2. Fill the tube until two inches from the top with 0.1 M NaOH solution, stopper the top end of the tube. 3. Rotate tube, remove the other stopper and fill with 0.1M HCL, stopper the end of the tube. 4. Rotate tube once. Diffusion will allow for the spread of ions across the solution, resulting in the production of a number of different colored pigments. Caution: Too much tube shaking will over mix the liquid and neutralize the solution.

3 5. Using the activity sheet, instruct students to record the colors found in the tube, noting color order and the color s relative positions to the HCL and NaOH. Some students may begin to recognize the scale that is created. Reinforce the idea of a color scale by displaying or passing around copies of known ph color scales, such as those found in a chemistry textbook. Homework: If students are unable to complete Section 1 of the activity sheet in the allotted class time, they should complete it for homework. OUTLINE OF THE PROCEDURE -- DAY 2 The following research will encourage self-discovery and establish a global connection to the data that students collected on day one. Using their data and elibrary, students will complete the activity sheet. Again, detailed instruction shouldn t be necessary beyond an introduction to elibrary, which, in turn, will provide the necessary resources for students to discover the sheet s answers themselves. Next, students in groups of 2-3 will explore articles provided by the teacher in an elibrary BookCart. Here s how to reach the BookCart for this unit, then copy and edit it to begin using it with your students. 1. Access the BookCart Editor and log in using your user name and password At the top, enter these search terms in the following fields: title: SBLA Cabbage Colors & Acid Rain author: ProQuest 3. Click the search button. 4. The SBLA BookCart will appear. Click the small box on the right under select, then click the copy button in the upper right-hand corner. 5. Change the title (remove copy of), description (optional) and add any other resources you d like (optional), then click the green save bookcart button. 6. The new BookCart will now be live on your local site and available to your students from the elibrary search page.. Students can find your new BookCart by clicking the bookcart link in the upper right-hand corner of any elibrary screen, then click next at the bottom to navigate through the BookCarts which are listed in alphabetical order.... SBLA Cabbage Colors & Acid Rain. Note: Students will be guided in their research using the activity sheet. ASSESSMENT Students will be evaluated based on student s use of elibrary to collect information and successful complete the activity sheet.

4 OPTIONAL EXTENSIONS Organize students to debate potential governmental solutions for reducing acid rain. Find maps on elibrary that suggest high-risk areas for acid rain. Research any natural solutions to acid rain. Brainstorm or research how acidity affects the reproduction and survival of organisms (e.g., frogs or city-dwelling humans).

5 CABBAGE JUICE & ACID RAIN A Science Lesson Student Orientation & Instructions Introduction: Is it really possible to show a relationship between cabbage juice and acid rain? You bet it is! In the following experiment, you will work in groups to create your own natural, dynamic and vibrant ph scale using red cabbage juice. You will then use various resources -- including elibrary -- to help answer the questions that follow. Background: Did you know that the pigments that control human skin color also control the color of plants? The most common plant pigment is chlorophyll, which is green. As you might expect, the plants that aren t green use a number of different pigments to provide their color. What s the wildest color you ve seen on a plant, fruit, flower or vegetable? One pigment found in cabbage juice in anthocyanin. This pigment will react with hydroxide and hydrogen ions in several different ways; depending on which ions are present (and in what concentration), anthocyanin s color will vary! Materials: One glass tube with stoppers on both sides ~200ml of cabbage juice (depending on the size of the glass tube) 10ml of 0.1 M NaOH (or other base) 10ml of 0.1 M HCl (or other acid) Procedure: 1) Take the glass tube and plug one end of the tube with a stopper. 2) Carefully add enough cabbage juice to the tube, being sure to leave enough space at the tope for the later addition of the acid and base. 3) On top of the cabbage juice add 10 ml of 0.1M NaOH. 4) Plug up the end. 5) Flip tube over and remove stopper. 6) Pour in the final 10ml of 0.1 HCL. 7) Plug both ends and lay the glass tube on surface. Make sure it can t roll. 8) Record what happens!

6 (Page 2 -- Cabbage Juice & Acid Rain) Data: Fill in the chart, indicating which color you believe represents various ph levels. COLOR ph Level Section I Questions Groups should make certain that all group members agree before writing down the answer to any question. a. Which solution, NaOH or HCL, is an acid? a base? b. In which solution is the concentration of hydroxide ions greater than the concentration of hydrogen ions? c. In which solution is the concentration of hydrogen ions greater than the concentration of hydroxide ions? d. Approximate the relative concentration of hydrogen and hydroxide ions in water. e. Using the information gathered in your data table, what color would the tube be if you shook it several times and allowed it to stand overnight? Explain in terms of hydrogen and hydroxide ions. f. Define the term acid : Define the term base : Section II -- GLOBAL CONNECTION 1. Go to elibrary 2. Click on the word bookcart in the upper-right corner of the screen 3. Scroll down to SBLA Cabbage Color & Acid Rain (Note: you may have to navigate through several screens of bookcarts using next at the bottom.) 4. Click on the bookcart title to open it

7 5. Browse the articles and websites and then select multiple ones that address the worksheet questions and your interest in this topic 6. Click on + add to my list for 3 or 4 resources that you consider to be most relevant to your assignment 7. You can save these to a disk or a school network student account, or them to your home, or print these 8. You can print MyList as your bibliography by clicking on my list (next to bookcart) You might already know the answers to some of the following questions; if so, that s great. However, for many of these questions you will probably need to use the learning resources you collected from the BookCart. Make sure you cite the sources you use to find your information. Use your data and the resources from elibrary to answer the following questions: a. What color would cabbage juice turn if it were mixed with an acid rain sample? Explain. b. Acid rain is associated with sulfuric and nitric acid. From what compounds do these acids form? c. Identify three potential sources of these compounds. d. Write out three reactions involved in the transition of sulfur (S) from a solid to sulfuric acid. e. Identify three environmental concerns relating to acid rain. What problems might they pose to our natural environment?

8 f. Brainstorm and list five ideas that your group hopes will help decrease acid rain. g. What are three national and international economic obstacles that delay progress on solving the problem