Chemistry Reference
In-Depth Information
demonstrations were shown in the past and are shown today to the public - mostly
in the area of physics and chemistry.
Liebig held evening lectures at the University of Munich/Bavaria in the years
around 1853 with spectacular demonstrations, so that even the king and the queen
of Bavaria came as guests. One evening the queen was so surprised by the beautiful
blue flash of the nitric oxide-carbon disulfide reaction (E2.5) that she wanted to see
it again. She asked Liebig to repeat this experiment, but the glass flask exploded due
to the mistake of his assistant (he filled the round flask with oxygen and carbon
disulfide - see E2.5) and all three, the king, the queen, and Liebig were wounded
[
12
]. Today we use upright cylinders and not round flasks for those reactions: the
explosion will never destruct a cylinder!
Our students may also want to see beautiful or spectacular experiments a number
of times, so we should plan for their safe repetition in the classroom. Concerning
these show experiments there are two different concepts. First, like the above-
mentioned nitric oxide-carbon disulfide reaction, these experiments are an event
and supposed to entertain people - they are not explained or interpreted scientifi-
cally. These experiments will mainly provide extrinsic motivation, they are suitable
for “Christmas Lectures” or other experimental shows - many topics are available
for those shows (see [
12
]or[
13
]).
On the other hand, show experiments can also be used scientifically. If facts
about “density of different substances” are introduced, then the usual mass and
volume measurements on metal samples can be performed, and the metals can be
identified from the table of densities. For a better motivation, the density issue can
also be introduced by an effect that students probably do not know. A tin of “Coca
Cola” and one of “Diet Coke” of the same size (330 mL) are placed in ice-cold
water: the first can sinks to the bottom of the glass bowl, the second one floats on top
(see E2.6). If a little story would be told to this effect that - at the last party - you
have to grasp very deep into the cold water when someone wants “Coca Cola,”
while “Diet Coke” simply is to be taken from the water surface, then the students
are even more motivated to think about this effect: it causes motivation through
reference to everyday life. The debate about the different densities will eventually
discuss the sugar contents: one can of “Coca Cola” contains about 20 g of sugar,
“Diet coke” only a small amount of sweetener.
Three other effects, which can trigger a substantive motivation, might be men-
tioned: the experiment “Ice breaks a bottle” (see E2.7) is an experiment that can
show the anomaly of water and may lead to the discussion of the structure of ice.
“Black carbon from white sugar” (see E2.8) may take the issue of the composition
of sugar with carbon as one of the elements. The amazing effect “Electricity from a
lemon” (see E2.9) sparks the discussion of the electrochemical potential series of
metals. Similar motivating experiments can be found for nearly any issue - the
creativity of the teachers is not limited in any way!
Hands-on with experimental or model material.
Especially for children, but also
for young students it is always important that they do not have to sit down quietly on
their chairs in school, but be allowed to move, to run around, or do something
manually: this is motivation in the
psychomotorical area
. For this reason, student
