Abstract:

As a continuation to our previous analysis, and having determined the alternative conceptions that Mexican students use to explain the thinning of the ozone layer, we designed a teaching-learning sequence (TLS), based on the criteria recommended in the literature (Sánchez Blanco & Valcárcel Pérez, 1993) that consisted of nine activities, which are explained below:
Activity 1 was a previous questionnaire, intended to know more about the alternative conceptions that the students had.
Activity 2 consisted of a video on the radiations of the electromagnetic spectrum and their characteristics. Both activities were left as homework before beginning the explanation before the group.
Activity 3 was a brainstorming to remember the radiations’ characteristics and next, activity 4 consisted of letting students use a simulation from the University of Colorado, on types of electromagnetic radiation and their interaction with some molecules.

In the second session occurred activity 5 where students were given data, with which they plotted height versus temperature, to identify the layers of the atmosphere. Likewise, the photochemical reactions involved in the formation and natural destruction of stratospheric ozone (Chapman cycle) and tropospheric ozone (photochemical smog) were explained to the group, taking advantage of the graph they performed (activity 6).

During the third session, the photochemical reactions involved in the catalytic destruction of ozone due to the presence of CFC were reviewed, including the reading of an article about the research of Molina and Sherwood (activity 7).

Subsequently, in the fourth session, the group was divided into teams, to hold a debate on whether Mexico should or should not, sign the Montreal Protocol, temporarily located in the 1980s (activity 8). The latter constituted the closing activity, and with it, the students were asked to give arguments, using what they learned during the implementation of the TLS.

Finally, it was left as homework for students to answer the questionnaire of activity 1 again, in order to compare the explanations they offer and verify if there were any changes. We applied the sequence to a group of 37 students of Chemistry III of high school, in a total of four fifty-minute sessions.

Keywords:

Undergraduate education, ozone layer depletion, alternative conceptions.