GREENHOUSE LAB EXPERIMENTAL FOUNDATIONS OF GLOBAL CLIMATE CHANGE BROUGHT ON BY CARBON DIOXIDE POLLUTION STUDENT VERSION: PART 1...1-10 PART 2...11-14 PART 3...15-17 TEACHER INFORMATION PAGES: PART 1...18-26 PART 2...27-28 PART 3...29-30 UV-Vis Instructions...31-33
EXPERIMENTAL FOUNDATIONS OF GLOBAL CLIMATE CHANGE BROUGHT ON BY CARBON DIOXIDE POLLUTION PART 1 STUDENT HANDOUT ARE LIVING ORGANISMS SOURCES OR SINKS FOR CARBON DIOXIDE GAS? Purpose: To use the color indicator bromthymol blue to determine if plants, animals and decomposers release carbon dioxide gas and to determine if plants absorb carbon dioxide gas. Background information: Are living organisms a source of carbon dioxide gas? Anything in nature, whether living, dead, or never alive (like a rock) is considered a source if it releases carbon dioxide into the atmosphere. Conversely, anything living or nonliving that takes up or absorbs carbon dioxide gas from the atmosphere or water is considered a sink (because like a sink in your home, it acts like a "holding reservoir" for carbon dioxide gas). This investigation involves the detection of carbon dioxide gas. How can you detect the presence of a gas that is colorless, odorless and tasteless? One method is through the use of a chemical indicator called bromthymol blue. Bromthymol blue is normally a blue liquid. If a small amount of carbon dioxide is added to it, the liquid turns blue-green to green. High levels of carbon dioxide gas cause the liquid to turn yellow. If the carbon dioxide is removed, the liquid will return to the blue color. The use of the spectrophotometer can quantify the color change. Materials (per group): test tube rack 9 medium test-tubes 1 hole stopper, connector and tubing 3 cotton balls Scissors Masking Tape Rubber stoppers Drinking Straw Pasteur Pipet Paper cup or beaker 0.1% Bromthymol Blue Solution 0.005% Bromthymol Blue solut n Vinegar Baking soda Yeast Solution Elodea Plant Plastic spoon Aluminum foil Metric ruler Forceps Light Source Chemistry Greenhouse Lab, Page 1 4/26/01
Procedure: Part A: Detecting the presence of Carbon Dioxide 1. Place two test tubes in the rack and label them A and B. 2. Fill test tube A 1/4 full with vinegar. 3. Fill test tube B 1/4 full with 0.005% bromthymol blue solution. Record its color in Table 1.1, Part A, "Initial Color". 4. Wrap a 1" x 1" piece of aluminum foil around the point end of a pen or a pencil. Twist the foil at the pointed end of pen of pencil so that you have created a little "cup" that will hold the baking soda. See Figure 1.1. 5. Using a plastic spoon, fill the aluminum "cup" half full with baking soda. See Figure 1.2. 6. Tilt the test tube at an angle that will allow the "cup" filled with baking soda to slide down into the test tube with Chemistry Greenhouse Lab, Page 2 4/26/01
vinegar so that the "cup" does not get any vinegar into the "cup". See Figure 1.3. 7. Place a cotton ball into test tube A about 1 cm from the top. Then, place the rubber stopper (with tube attachment) into test tube A. See Figure 1.4. 8. Submerge the free end of the rubber tube into the bromthymol blue solution of Test Tube B. Place a cotton ball at the top of test tube B to hold the tubing in place. See Figure 1.5. Your completed set-up should look like Figure 1.6. Before continuing predict what color the bromthymol blue solution will be after the baking soda mixes with the vinegar. Record your prediction in Table 1.1, Part A, "Predicted results". Chemistry Greenhouse Lab, Page 3 4/26/01
10. Rock test tube A from side to side (do not shake up and down) mixing vinegar with baking soda. See Figure 1.7. 11. Note the production of gas (bubbles of carbon dioxide gas, CO 2 ). After three minutes of bubbling in test tube B, record the color of the solution in Table 1-1, Part A, "Observed results". Chemistry Greenhouse Lab, Page 4 4/26/01
Part B: Determining if plants are a source for carbon dioxide. 1. Place two clean test tubes in the rack and label one tube C and the other D. Place a 5.0 cm segment of Elodea (the aquarium plant) into the bottom of tube D. You may need to push the plant down with a pencil to get the plant to the bottom of the test tube. 2. Fill test tube D with enough 0.005% bromthymol blue solution to cover the Elodea plant. Fill test tube C to the same level. Test tube C should contain only bromthymol blue solution. Label each test tube with your name and contents (masking tape may be used), and seal with rubber stoppers. 3. Wrap each tube separately in a sheet of aluminum foil so that no light gets into the tube. Label with masking tape with your name. Store tubes per your instructor's directions. Predict the color of the bromthymol blue solution in each tube after 24 hours. Record the color in Table 1.1, Part B, "Predicted results". 4. After 24 hours in the dark, unwrap your tubes and note the color of the liquid in each tube. Record the color in Table 1.1, Part B, "Observed results". You may find it helpful to place a sheet of white notebook paper behind the tubes to compare the colors. It may also be helpful to remove the Elodea from the test tube. Chemistry Greenhouse Lab, Page 5 4/26/01
Part C: Determining if decomposers are a source of Carbon Dioxide. 1. Place two clean test tubes in the rack and label one E and the other F. Fill both test tubes about 1/4 full of 0.005% bromthymol blue. Record the color of the solution in Table 1-1, Part C. 2. Using a Pasteur pipet, add 10 drops of yeast solution to tube F. Add no yeast solution to tube E. With masking tape, label each tube with your name and contents of each tube, and seal tubes with rubber stoppers. 3. Predict the color of the bromthymol blue solution in each tube after exposure to the yeast. Record the color in Table 1.1, Part C, "Predicted results". 4. Place tubes in teacher-designated area. 5. At the end of the period, note the color of the liquid near the bottom of each tube. Place a sheet of white paper behind the tubes if necessary. Record the color in Table 1-1, Part C, "Observed results". Part D: Determining if animals are a source of Carbon Dioxide. 1. Place about 50 ml of distilled water in a beaker. Place one drop of the water on a spot plate or glass slide. Add one drop of 0.005% bromthymol blue solution and note the color. Record the color of the liquid in Table 1-1, Part D, "Initial color". 2. Predict the color change that the bromthymol blue test will cause in the distilled water if you blow bubbles into the water. Record your "Predicted Results" in Table 1-1, Part D, "Predicted results". 3. Exhale gently through a straw into the water so that your breath bubbles through the water. Do this for several minutes, then test by placing one drop of the water on a spot plate or glass slide and adding one drop of 0.005% bromthymol blue solution. Note the color. If the water does not test yellow, continue exhaling into the beaker for another minute or two, and test again. 4. Record the color of the liquid in Table 1-1, part D, "Observed Results". 5. Save the distilled water that you exhaled into for part E. Chemistry Greenhouse Lab, Page 6 4/26/01
Part E: Determining if plants are a sink for carbon dioxide. 1. Fill 3 test tubes equally with the solution from part D. Label the test tubes G, H, I. 2. To test tubes G & I, add a 5.0 cm sprig of Elodea plant. Use your straw to push the plants down to the bottom of the test tubes. Seal the tubes with a rubber stopper. 3. Seal test tube H with a rubber stopper (NO PLANT). 4. Wrap test tube I entirely with aluminum foil to make it light tight. 5. Place all three test tubes in a rack. Expose the rack of test tubes to a light source for at least 24 hours. 6. For each of the 3 test tubes predict the color of the solutions when tested with bromthymol blue at the end of the 24 hour experimental period. Record in Table 1-1, "Predicted Results." 7. After 24 hours, uncover the foil wrapped test tube and add ten drops of 0.1% bromthymol blue solution to each test tube (G,H,I). Compare the shades of color by holding test tubes against a white background. Record your results in Table 1-1, "Observed Results". Chemistry Greenhouse Lab, Page 7 4/26/01
Observations: Table 1-1 DATA CHART PART TUBE INITIAL COLOR PREDICTED RESULTS OBSERVED RESULTS Part A Detection of CO 2 Part B Plants as source of CO 2 Part C Decomposers (Yeast) as source of CO 2 Part D Animals as source of CO 2 Part E Plants as sinks for CO 2 Tube B + gas from Tube A Tube C only Tube D + Elodea Tube E only Tube F + Yeast Cup + Exhaled Breath Tube G Liquid from Pt. D & Elodea Tube H Liquid from Pt. D & no plant Tube I Liquid from Pt. D + Elodea in dark Chemistry Greenhouse Lab, Page 8 4/26/01
Discussion/Conclusion: 1. List the organisms in this lab that were found to be a source for carbon dioxide? 2. Explain how one can experimentally detect the presence of carbon dioxide. 3. Are plants a source of carbon dioxide? What is your evidence? 4. Are animals a source of carbon dioxide? What is your evidence? 5. Are decomposers a source of carbon dioxide? What is your evidence? 6. What is the purpose of having only Bromthymol Blue in test tubes C and E? Chemistry Greenhouse Lab, Page 9 4/26/01
7. Why did the bromthymol blue turn light-green when you blew into the blue solution? 8. How are you certain that light itself is not responsible for the bromthymol changing back to the blue color? 9. Explain the reason for the color observed at the end of the experiment in test tube I. 10. Are plants a sink for carbon dioxide? What observed evidence do you have? Explain. 11. Presently, certain countries are cutting down thousands of square kilometers of forests. Explain two ways this activity affects the amount of CO 2 in the atmosphere? Chemistry Greenhouse Lab, Page 10 4/26/01