Chemistry Reference
In-Depth Information
strip stays as before (Pb). The transformer is removed after a few minutes; the
voltage between the two strips is measured: about 2 V. An electric motor is
connected, which runs for a while and then stops (compare with E4.10).
E8.14 Flashing Cement “Ca(OH)
2
Type” Ingredients are checked on the label of
the container. The mixture of the substance with little water is tested with
indicator paper: alkaline reaction.
In a beaker, little water is given to fresh calcium oxide (Xi): increase of the
volume under hissing noises; strong exothermic reaction. The white product
is inspected with a wet strip of indicator paper: strong alkaline reaction.
The product (or calcium hydroxide (Xi) out of a supply bottle) is mixed with
water in an Erlenmeyer flask, carbon dioxide is added from a steel bottle and a
syringe filled with carbon dioxide is connected to the flask. The flask is moved
so that the mixture spreads inside the flask: the piston of the syringe moves;
the mixture heats up.
E8.15 Fire Extinguisher Model “Wet and Foam Extinguisher Type” Put on safety
glasses. A plastic spray bottle is filled to half with concentrated sodium
carbonate solution. A small test tube, which contains a few milliliters of
concentrated sulfuric acid, is put into the solution in a way that it swims. The
bottle is shut with a capillary glass tube. Close to a sink, the spray bottle is
briefly inverted; the spurt of the spray bottle is pointed into the drain: the
content of the extinguisher model empties itself with a cutting spurt. In a
repetition of this experiment, foam concentrate can be mixed to the sodium
carbonate solution: model experiment of a foam extinguisher. Caution in the
disposal: remains of concentrated sulfuric acid!
E8.16 Alcohol Test “Chromate Type” One alcotest tube is prepared; a small
amount of alcohol is spread in the mouth and ethanol vapor is blown with
the breathing air through the tube into a synthetic plastic bag: the color in the
indicator zone turns from yellow to green.
A yellow-colored potassium chromate solution (T/N) is acidified, and a
small amount of ethanol (F) is added: a color change from yellow to orange
occurs first, then the change from orange to green is observed.
References
1. Waddington D (2000) The Salters Chemistry Project: 15 years on. Presentation during the 15th
Symposium of Chemical Education in Dortmund/Germany, University of York, 15 June 2000
2. Barke H-D (1987) Chemieunterricht erscheint nicht so sinnlos, wenn man den Stoff auch im
Alltag anwenden kann. In: Lindemann H Alltagschemie. NiU P/C 35:Heft 25
3. Gesellschaft Deutscher Chemiker (1992) Denkschrift zur Lehrerausbildung f
€
ur den Chemieun-
terricht auf der Sekundarstufe II. Frankfurt
4. Pfeifer P, Haeusler K, Lutz B (1992) Konkrete Fachdidaktik Chemie. Oldenbourg, M
unchen
5. Barke H-D (1996) Lebenswelt und Alltag im Chemieunterricht. In: Behrendt H Zur Didaktik
der Physik und Chemie. Leuchtturm, Alsbach
€
