Carbon Dioxide - Sources and Sinks

In this lab activity, students use a chemical indicator (bromothymol blue) to detect the presence of carbon dioxide in animal and plant respiration and in the burning of fossil fuels and its absence in the products of plant photosynthesis. After completing the five parts of this activity, students compare the colors of the chemical indicator in each part and interpret the results in terms of the qualitative importance of carbon sinks and sources.

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Activity takes about three 40-min lesson periods and some preparation. Additional materials required.

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Teaching Tips

Teaching Tips

The educator should be well informed about the carbon cycle, sources and sinks. See, for example, this site from Vision Learning:

Activity is very focused on the mechanics of the experiments and doesn't require the student to understand the bigger picture and the reason for doing this experiment. Educator should include a teaching unit on the carbon cycle to tie this experiment into the bigger picture.

Teacher prep time is extensive. The activities require equipment and supplies commonly found in a chemistry lab, except for the indicator Bromothymol blue and a sprig of Elodea (available in pet stores as an aquarium plant).

There are six test tubes involved:
A: control - 1/3 full of BTB;
B: test for Part 1 - 1/3 full of BTB;
C: test for Part 2 - 1/3 full of BTB;
D: test for Parts 3 and 4 - 1/3 full of BTB, wrapped in foil, sprig of Elodea;
E: test for Part 5 - 1/3 full of BTB;
unmarked: vinegar and baking soda.

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