Item #: PF2065
In this lab experience, students investigate the three main sources of anthropogenic carbon emissions: combustion, land-use/deforestation and cement production. They also develop a model to describe the cycling of carbon among the hydrosphere, biosphere, geosphere and atmosphere and learn that matter, such as the C atoms in CO2, cannot be created or destroyed, only converted from one form to another. In Part A, students combust a hydrocarbon (a candle) and observe that the CO2 produced is absorbed by a solution of basic water and phenolphthalein, because the solution turns from pink to colorless as the H2CO3 produced lowers the pH. In Part B, students see that an Elodea sprig in water exposed to light reduces the concentration of dissolved CO2 and thus raises the pH. Students use bromthymol blue to observe indirectly the conversion of dissolved CO2 to glucose. In Part C, students heat a metal carbonate to its decomposition temperature to simulate the curing of concrete. When students heat the metal carbonate they observe indirectly the production of CO2 because it changes the color of an aqueous acid–base indicator owing to the formation of H2CO3.
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