Chemistry Reference
In-Depth Information
Material: Two 50 mL-measuring cylinders, two glass tubes of the same
lengths (Ø: 8 mm and 6 mm); diluted copper sulfate solution (Xn)
Procedure: One of the cylinders is to be filled with 50 mL of the blue
solution, the other cylinder remains empty. Two glass tubes of the same
diameter are used to lift and carry the solution from one cylinder to the
other, until the volumes are equal in both cylinders. This experiment is to be
repeated with glass tubes of different diameters. The volumes and the
corresponding number of lifting processes can be illustrated in a chart.
Observation: Equal volumes only result in the first case. In the second case
the volume ratio is for example 35:15. The volumes remain on this level
even with further lift processes.
E4.3. Projection of electrolysis experiments
Problem: When the illumination of an apparatus does not improve the
observation for the student, it is possible to project phenomena with the
overhead projector, as long as they take place in transparent solutions.
Especially when new substances only originate in small amounts, like
during electrolyses, the projection is a good way to magnify the reaction
dish and to make the electrolysis observable for all students.
Material: Petri dish, two pieces of platinum wire, transformer and cable;
zinc bromide solution.
Procedure: The two pieces of platinum wire (the electrodes) are to be
attached to the Petri dish and with the cables connected to the transformer's
direct current poles. The Petri dish is to be put on the projector and the
bottom is to be filled with zinc bromide solution. A direct current of about
5-10 V is to be set.
Observation: One can directly observe the precipitation of yellow bromine
on the positive pole and the creation of zinc crystals on the negative pole.
With the right voltage it is possible to see the growth of a “zinc tree”. This is
better visible with the help of the overhead projection.
E4.4. Experiments in the projected Petri dish
Problem: Many reactions take place in colored solutions; these colors can
be made visible if light shines through the solution. Since there is an
overhead projector in every chemistry class room, Petri dishes, especially
the ones with three compartments, are interesting for showing colored
solutions and their reactions. Different reactions can be observed at the
same time.
Material: Tripartite Petri dish, pipet; acid-base indicator (F), hydrochloric
acid (C), sodium hydroxide solution (C)
Procedure: The three compartments of the Petri dish are to be filled with an
indicator solution, for example universal indicator dissolved in tap water:
this solution is green. One drop of hydrochloric acid is to be added to the
first compartment, one drop of sodium hydroxide solution to the second
compartment. One drop of the acidic or basic solution can be used to
neutralize the solutions in both compartments of the Petri dish.
