Earth Systems
Standard 5: Objective 1
Title: Carbon Cycle Sources & Sinks
A Brief Description: Students will use the chemical indicator bromothymol blue to detect the presence of carbon in different sources.
· Experiment 1: students will gain experience in detecting CO2 through the BTB reaction by using a pure CO2 gas made from the reaction of baking soda and vinegar
· Experiment 2: students will determine if animals are a source of CO2
· Experiment 3: students will determine if plants are a source of CO2 (through respiration)
· Experiment 4: students will determine if plants are a sink for CO2 (through photosynthesis)
· Experiment 5: students will determine if fossil fuels are a source of CO2 (this is an extremely effective demonstration when done correctly)
Objective: Students will identify the sources of carbon in the carbon cycle.
Materials needed: Test tube rack, 5 test tubes, one hole stopper with tubing attached, baking soda, vinegar, aluminum foil, cotton balls, bromothymol blue, straws, Elodea plant, overhead markers, balloons, manila file folder, oven mitt, plastic grocery bag with no holes
Time Needed: Materials preparation: 30 minutes
Class time: 40 minutes (with one observation 24 hours later)
Discussion & review: 30 minutes
Safety/Security Issues: Carbon monoxide is an odorless, moderately toxic, poisonous, and flammable gas. In a well-ventilated room, students could do this activity. In that case, teachers should provide students with balloons full of car exhaust. It is not recommended that students participate in filling the balloons with car exhaust. An adult assistant (or two) is necessary, however.
Teacher Procedures:
1. Gather materials. You can choose to make stations for each experiment, or to provide materials for each lab group in your classroom.
2. Hand out the student sheets and go over the directions with students.
3. Give students an opportunity to work.
4. At some point, do the teacher demonstration for Experiment 5.
5. After the experiments & demonstration are done, give students time to work on analysis & conclusion.
Preparations for Experiment 5, Teacher Demonstration
Automobile exhaust collection
1. Get a plastic grocery bag, rubber band and oven mitts.
2. Place the rubber bag around the mouth of the bag but do not tighten it.
3. Using the heat resistant mitts, approach the exhaust pipe from the side. Place the opening of the bag over the tail pipe. Use the gloved hand to help form a seal between the it and the exhaust pipe. The bag should fill quickly when an assistant starts the car. When the bag is filled pull the bag off and use the rubber band up to seal the bag.
Experiment 5, Teacher Demonstration Procedures:
1. Fill test tube E approximately 1/3 full of bromothymol blue.
2. Take the exhaust filled bag, carefully place a straw in the rubber band so that the gas does not escape.
3. Insert the straw into test tube E.
4. Gently release air from the bag by slowly pressing on the sides. Allow the gas to bubble out at a steady rate until the balloon is empty.
5. Have students record observations.
Title: Carbon Sources & Sinks Name______
Background: Carbon atoms cycle through Earth’s atmosphere, biosphere, geosphere, and hydrosphere. Each stop carbon makes is considered a source or sink of carbon. The amount of carbon in each sink varies as well as the amount of time carbon will spend in each sink.
Bromothymol blue is a chemical that indicates the presence of carbon dioxide. If carbon dioxide is present, bromothymol blue solution will turn greenish yellow. The lighter the bromothymol blue becomes, the more carbon is present in the solution.
Materials: Test tube rack, 5 test tubes, one hole stopper with tubing attached, baking soda, vinegar, aluminum foil, cotton balls, bromothymol blue, straws, Elodea plant, overhead markers
Procedures:
1. Work in groups and follow the instructions carefully for each experiment.
2. Record data for each experiment.
3. Answer the analysis questions.
Experiment 1: Detecting CO2 Gas
Materials: masking tape, test tube rack, 3 test tubes, labeling marker, 1 square inch of foil, vinegar, bromothymol blue, baking soda, cotton ball, rubber stopper with tubing
1. Using an overhead marker, label 4 test tubes A thru D. Leave the 5th test tube unmarked. Place all test tubes in the test tube rack.
2. Fill test tubes A & B 1/3 full with bromothymol blue. (Test tube A is the control test tube.)
3. Fill the unmarked test tube ¼ full of vinegar.
4. Using the foil, make a small “boat” for the baking soda (see Diagram A). Be careful not to poke a hole in the foil.
5. Fill the foil boat ½ full of baking soda.
6. Carefully slide the foil boat inside the unlabeled vinegar test tube. Tilt the test tube a little to make it easier. Be very careful, you don’t want any baking soda to get into the vinegar yet. (See Diagram B)
7. Place the stopper in the vinegar test tube once the foil boat is floating in the vinegar.
8. Place the other end of the rubber tubing into test tube B. Make sure the tubing touches the bottom of the test tube. Stuff the cotton ball in the neck of test tube B so that air won’t go in or out. (See Diagram C)
9. Mix the vinegar and soda together by GENTLY swirling the tube from side-to-side. Don't shake it upside down!
Data: Record observations below.
Experiment 2: Are animals a source of CO2?
Materials: 1 test tube, bromothymol blue, straw
Procedures:
1. Fill test tube C 1/3 full of bromothymol blue.
2. Place a straw in the test tube and gently blow. (Be careful not to suck any bromothymol blue up!)
Data: Record observations below.
Experiment 3: Are plants a source of CO2?
Materials: 1 test tube, bromothymol blue, piece of Elodea plant, aluminum foil
Procedures:
1. Fill test tube D 1/3 full of bromothymol blue
2. Place a piece of Elodea plant in the test tube. (Use a pencil or pen to push it all the way into the bottom of the tube)
3. Wrap the tube in foil so that no light can get in.
4. Place in test tube rack and leave for 24 hours.
Data: Record observations below.
Experiment 4: Do Plants take up CO2?
Materials: test tube with Elodea from Experiment 3, heat lamp
Procedures:
1. Unwrap test tube D.
2. Place the test tube near a heat lamp and leave it for about 20 minutes.
Data: Record observations below.
Experiment 5 (Teacher Demonstration): Are Fossil Fuels a Source of CO2?
Procedures:
1. Watch the demonstration given by your teacher.
2. Record observations in the data section.
Data: Record observations below.
Analysis:
1. Compare the colors in the tubes A-D and test tube E from your teacher’s demonstration. What does the color of the solution tell you?
2. If you wished to reduce the amount of increase of carbon in the atmosphere, which source would be most important to control? Explain why.
3. Would there be problems with controlling the things you mentioned in question 1? Why or why not?
4. Do plants produce carbon dioxide? Explain why or why not.
5. Describe the role of fossil fuels in the carbon cycle.
6. What are the sources of carbon?
7. Write a brief description of an experiment that tests for carbon in another source.
Conclusion: Write 2-3 things you learned in complete sentences.