Chemistry Reference
In-Depth Information
substances might additionally contain alcohol D
¼
propanol. It has to be made
clear that alcoholic beverages only contain ethanol.
- Spot remover does certainly not contain carboxylic acids, but at least one alcohol
and one ester. The following combinations are possible:
Combinations of two:
A/C
A/F
D/C
(not: D/F!)
Combinations of three:
A/C/D
A/F/D
D/C/F
A/C/F
Combinations of four:
A/C/D/F
- Nail polish remover no. 4 shows the same test results as spot remover. Different
household products might contain the same substances.
- Contrary to nail polish remover no. 4, nail polish remover no. 5 does not contain
any of the six substances A-F. Similar household products might contain
different substances.
- Additionally, it can be readily discovered effort that glue contains at least one
ester (positive Rojahn test) ([
1
], p. 315). A smell test with substance C indicates
that the glue contains ethanoic ethyl ester. This is confirmed by the positive
iodoform test. Note that the ester functions as a solvent, which evaporates when
the glue is being applied.
Testing household substances provides good opportunities to connect the system
building substances A-F with aspects of everyday life. Synonymous trivial names
that have to be learned should be added to the systematic names. The working
language should not disconnect itself from communication in everyday life, media,
and science:
A
¼
ethanol
¼
drinking alcohol (in alcoholic drinks)
B
¼
ethanoic acid
¼
acetic acid (in vinegar)
C
¼
ethanoic ethyl ester
¼
ethyl acetate (solvent for glue)
D
¼
propanol
¼
propyl alcohol (solvent for cosmetics)
E
¼
propanoic acid
¼
propionic acid (preserving agent for bread)
F
¼
propanoic propylester
¼
propyl propionate (nonpolar solvent)
The microbiological production of acetic acid can be discussed in detail in this
context: Ethanol is transformed by
Acetobacter
bacteria with the oxygen in air to
acetic acid. One hundred gram of vinegar contain about 5-15 g of acetic acid.
Vinegar essence contains 60-80 vol% acetic acid and therefore it is a highly
corrosive substance, which can only go on sale under safety measures. It is being
diluted with water to produce table vinegar.
Students should be told that for safety reasons only diluted acids are being used
in the student experiments in Sect.
9.1
.
The function of the dichromate reagent as an oxidizing agent can be understood
by comparing the microbiological acetic acid synthesis with the acetic acid synthe-
sis discovered in Sect.
9.2
(from ethanol and dichromate). Since the orange-colored
dichromate is being reduced to green-colored chromium salts, the students are now
able to understand the green coloration in the positive dichromate test.
