Chemistry Reference
In-Depth Information
Procedure: The cylinder is completely filled with water and with the help of
the stopper placed pneumatically in the glass bowl half filled with water.
Under the opened cylinder one mineral tablet is placed, and the produced
volume of gas is marked or recorded. A second tablet is placed in the same
way and the resulting gas volume is also recorded.
Observation: The gas volume of the first tablet may result in about 70 mL,
of the second tablet 70 + 130 mL: a total of 200 mL is observed (the actual
volumes differ according to the brand of the tablets, they should be tested
prior to use in the demonstration).
E2.4. Extinguishing Fires of Fat and Metals
Problem: Most fires in everyday life are extinguished with water. Therefore,
students are usually unaware that it is not possible to extinguish burning
metals, e.g., magnesium or burning fat with water - on the contrary, treating
these fires with water causes terrible accidents. The experiments can be
demonstrated either for a discussion of these safety aspects as well as a way
for students to create a cognitive conflict and to solve it. In the experiments
you can see that the burning fat at high temperatures of 300
C or more
evaporates the added water instantly and an explosive mixture of vaporized
fat and air burns with a big yellow flame. In the case of burning magnesium,
the vigorous reaction of the metal with water forms metal hydroxide and
hydrogen: this gas burns with a bright white flash. Instead of extinguishing
both flames they are increasing to big fires - you have to eliminate the air
from both fires, with sand in case of burning metals, and by closing the
container in case of the burning fat.
Material: Tripod and wire gauze; tea light with aluminum container, mag-
nesium turnings (F), deionized water bottle with water.
Procedure: (a) The wick of a tea light is cut off. The paraffin is heated
strongly in the aluminum container until smoke is produced by decomposi-
tion of paraffin and the smoke is ignited. A water jet is aimed directly onto
the burning paraffin. (b) A spoon of magnesium turnings are put together on
the wire gauze and ignited by the strong burner flame. A water jet is aimed
onto the burning metal (caution, wear goggles! For protecting the table
against burning spots, cover the table with aluminum foil).
Observation: (a) The burning fat creates an up to one meter high yellow
flash; (b) the burning magnesium forms a high, bright white flash.
E2.5. Blue Lightning Through Explosions of Gas Mixtures
Problem: A historic show experiment shall demonstrate that striking
experiments are usually associated with big emotions: even the Bavarian
Queen wished to see the “Blue Lightning” for a second time and Liebig
tried to perform the reaction of nitrous oxide and carbon disulfide again (see
Sect.
2.2
). Instead of nitric oxide he incorrectly used oxygen in the mixture
with carbon disulfide and the round flask exploded injuring the king, the
queen, and the experimenter himself. Today we use no round flasks for this
experiment, but cylinders with parallel glass walls: those explosions cannot
destroy the cylinder, the reactions are carried out safely.
