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Think-aloud methods in chemistry education
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Imagine you are teaching a first-term chemistry class. The class has discussed Lewis structures, and you have moved into intermolecular forces before leading into properties of gases. In lab the students have carried out a decomposition to demonstrate stoichiometric relations and recently have done a lab in which they collected a gaseous product over water. After several days working with the class discussing the behavior of gases, you ask them to work in small groups on the following problem:
Which is denser at the same temperature and pressure, dry air or air saturated with water vapor? Explain (1).
As you walk around the room and listen to the small groups working on this problem, you hear several approaches to working the problem.
The first group you see working on the task draws pictures as a way to represent the problem. At first they recall that air is mainly a mixture of oxygen (20%) and nitrogen (80%) so they draw two containers of air (shown in Fig. 1). (Fig. 1 omitted) Next, the students remember that Avogadro's law will help them figure out that if the containers are the same size (at the same temperature and pressure), then they have to have the same number of particles. So they modify one of their original drawings by reducing the number of oxygen and nitrogen molecules and replacing them with water (see Fig. 2). (Fig. 2 omitted) From this modified drawing they realize that, for a given volume, the overall mass of the moist air is less than the dry air (based on the total mass of molecules in their drawing). So this group of students concludes the moist air is less dense
As you continue to walk around the room, another group figures out a way they could go into a lab...