Chemistry Reference
In-Depth Information
Fig. 1.10
Concept cartoon concerning the conservation of mass [
19
]
have to be discussed in chemistry lectures, there are two hypotheses to influence
instruction: (1) one can discuss themisconceptions first and come upwith the scientific
explanation afterwards, (2) one teaches the scientific concept first and afterwards
students compare it with their own or other misconceptions from the literature.
Petermann, et al. [
22
] use the first hypothesis for their study concerning the well-
known preconcept of combustion: “Something is going into the air,
some things
are going away.” In their lectures they showed the burning of charcoal and
discussed alternative conceptions like: “charcoal is gone, some ashes remain.”
Afterwards they used the idea of a cognitive conflict: little pieces of charcoal are
deposited in a big round flask, the air is substituted by oxygen, the flask is tightly
closed and the whole assembly is weighed using an analytical balance. Pressing the
stopper on the flask and heating the area of the charcoal, the pieces ignite and burn
until no charcoal remains. The whole contents are weighed again, and the scales
present the same mass as before.
Working with this cognitive conflict the students discover that there must be a
reaction of carbon with oxygen to form another invisible gas. After testing this gas
using the well-known lime water test one can conclude: the gas is carbon dioxide.
...
