Chemistry Reference
In-Depth Information
Material: Glass cylinder with cover glass, glass bowl, large test tube with a
discharge pipe, plastic pipette (5 mL), burner, ammonium nitrate (O),
carbon disulfide (F/T), oxygen (O).
Procedure: In the preparation, ammonium nitrate is decomposed in a test
tube by gentle heating; the resulting colorless gas of nitrous oxide is
introduced pneumatically into the cylinder (under the exhaust hood!). The
pipette is filled with 2 mL of carbon disulfide and emptied into the cylinder;
the cylinder is covered with the cover glass. After removal of the cover the
mixture is ignited by the Bunsen flame. The experiment is repeated with
oxygen and carbon disulfide.
Observation: A light blue flash appears and a specific sound is heard
reminiscent of a barking dog (the experiment is therefore also called
“barking dog”). In the second experiment a white flash is seen, which is
accompanied by a loud bang.
E2.6. Diet Coke Is Lighter Than Coca Cola
Problem: The concept of density can be introduced by an effect, which
surprises most students and therefore challenges them to explain the effect.
Both cans are placed into ice-cold water: the can of Coca Cola drops down
to the bottom of the container, the can of Diet Coke swims.
You need to weigh both cans, to discuss the higher mass of 330 mL Coca
Cola and to interpret this according to the high content of dissolved sugar in
Coca Cola. Moreover, students are motivated to develop the idea of density:
Coca Cola has the higher density compared to Diet Coke or Cola Light.
Material: Large glass cylinder, balance, areometers (densities around
1.0 g/mL); 330 mL-can “Coca-Cola,” 330 mL-can Cola Light or Diet
Coke, ice water.
Procedure: The cylinder is filled to three quarters with ice water; both cans
are placed into the water. Then both cans are weighed. Both samples of coke
are heated to release the carbon dioxide; the densities of both solutions are
measured by an areometer.
Observation: The can of Coca Cola sinks to the bottom of the cylinder, the
can of Cola Light swims on the surface. The can of Coca Cola weighs about
20 g more than the can of Cola Light. The density of the Coca Cola is a little
bigger than 1.0 g/mL.
Note: The production technology of canned Cola causes an air bubble in the
can. These bubbles may differ from can to can and therefore the can of Cola
Light may also sink in water. Try out some cans and choose the right ones
before you show the experiment.
E2.7. Ice Lets a Bottle Burst
Problem: Another density phenomenon is provided by the anomaly of
water: ice occupies a bigger volume than a portion of water with the same
mass. We are very familiar with the fact that ice floats on water and we do
not think about the fact that normally the solids sink in their melts: a candle
sinks in its melt, a piece of lead sinks in the molten metal.
