Conceptest: CFCs and Ozone

David McConnell, Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University
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This material is replicated on a number of sites as part of the SERC Pedagogic Service Project
Initial Publication Date: November 30, 2008


Analyze the following student descriptions of the relationship between CFCs and ozone. Which is the best?
a. CFCs are manufactured gases that destroy the ozone layer and produce oxygen.
b. Chlorine forms from the disintegration of manufactured gases. The chlorine reacts with ozone molecules to form two gases that can not block incoming UV radiation.
c. Oxygen molecules are broken down by UV radiation to free oxygen atoms that combine with chlorine monoxide to form new oxygen molecules and free chlorine. Chlorine helps break down CFCs with UV radiation.
d. UV radiation breaks apart complex manufactured chlorofluorocarbons into its constituent atoms, including chlorine. Chlorine destroys ozone molecules as it cycles through a pair of reactions that produce free oxygen molecules.

Student Responses:

Student responses to this question were collected from large (60+ student) introductory Earth Science classes populated by non-majors (mostly freshmen) at an open enrollment Midwestern university. N=163 on first attempt; N=167 after peer instruction)
a. 13% of students chose this answer on their 1st attempt; 0% after peer instruction.
b. 19% of students chose this answer on their 1st attempt; 14% after peer instruction.
c. 26% of students chose this answer on their 1st attempt; 9% after peer instruction.
d. 42% of students chose this answer on their 1st attempt;77% after peer instruction.(correct)

References and Notes: