Learners Ideas and Misconceptions - Essentials of Chemical Education - page 11

Fig. 1.5 Masses before and after combustion of phosphorus [ 8 ]
“Nothing in the container could escape, but the phosphorus has been destroyed and
the smoke dissolved making it weigh less” [ 8 ].
Barke [ 7 ] asked students about the equation representing the combustion of
magnesium and most of the grade 10 students answered correctly (see Fig. 1.6 ).
Because they knew the atomic model and the idea about atoms, ions, and molecules
students were asked to describe “what happens to the small particles of magnesium
during combustion” (see Fig. 1.6 ).
Some students answered the question in this way: “magnesium contains two
kinds of particles, one evaporates by combustion, the other one remains as magne-
sium oxide.” They even drew their imagination in the same way (see Fig. 1.6 ). This
example shows that students learn the equation only formally, but keep their mental
model from everyday life that they developed in 10-15 years of observations.
Teachers should know that they cannot effect complete conceptual change from
students' preconcepts in 1 or 2 h of instruction: for several weeks one has to show
new experiments concerning combustion. The observations have to be explained
with oxygen reactions to metal or nonmetal oxides, and one has to visualize the
structure of substances before and after oxidation with sphere packing or model
drawing [ 8 ].