Experiments - Essentials of Chemical Education - page 133

Table 5.3 Fulfillment of criteria 1-12 for choosing initial experiments on chemical reactions
Examples from school topics 123456789012

Formation of Iron sulfide xxxx x xxx

Copper sulfide xxxxxxxxxx
Metal oxides xxxx x xxxxx
Nonmetal oxides xxxx x xxxx

Metal chlorides x x x x x x x x

Aluminum bromide xxxx xxx

Silver iodide xxxxxxx xxx

Sodium amalgam xxxxxxxxxx

Element A + Element B ! Compound AB; energy turnover

1. A, B, AB should be familiar to the students from their everyday life.
2. The reaction should be possible as a student experiment.
3. The reaction should run in a suitable period of time.
4. The experiment should not need too much instrumentation.
5. Substances A, B, AB should be visibly solid or fluid.
6. A, B, AB should be obviously distinguishable by their properties.
7. The mixture of A and B should be easily separable.
8. AB should react back into its elements.
9. The reaction should show a distinct energy turnover.
10. Safety rules must be performed.
11. A and B should be visualized by models (sphere packing or molecular model).
12. AB should be visualized by models (sphere packing or molecular model).

Conduct of experiments: The most frequently used form of experimentation at
school is the demonstration experiment. Although the student experiment is con-
sidered to be educationally important and valuable, due to lack of time or unsuitable
equipment it is not always realized. A compromise between both can be an experi-
ment demonstrated by students: one student or a group of students prepare and
demonstrate an experiment to the class (see Table 5.4 ).
To draw the observer's attention to the essentials and to optimize the perception,
a few principles of Gestalt psychology need to be considered for demonstration
experiments [ 18 ]:

- Parts of an apparatus are to be arranged in such a way that substances flow from
left to right for the viewer
- Stands should not disturb the observation of planned effects, they are to be put
behind the apparatus from the viewer's perspective
- Apparatuses are to be as easy as possible, needlessly complicated vessels or
equipment should be avoided
- Connection tubing should be arranged flat and horizontal, the substance flow
should run in a straight line
- Objects or chemicals, which do not immediately belong to the experiment, are to
be removed from the table of the experiment
- Planned effects are to be visually, acoustically or olfactorily intensified, if
otherwise they cannot be observed sufficiently from the distance