Chemistry Reference
In-Depth Information
Fig. 9.12
Mixing other alcohols with water in Petri dishes in overhead projection [
13
]. 1 =
butanol, 2 = pentanol, 3 = hexanol, 4 = octanol
9.8.3 Many Ways Lead to Acetic Acid
Synthesis experiments can be effectively used for a further integration of knowledge.
A whole range of substances can be converted into acetic acid with the help of the
dichromate reagent ([
1
], p. 239): ethanol, acetaldehyde, acetal, ethanoic ethyl ester,
pyruvic acid, lactic acid, acetone, and malonic acid (Fig.
9.13
). Acetic acid can be
identified in the distillates with the help of the BTB and the iron chloride test. Note that
for the oxidation of acetone to ethanoic acid stronger reaction conditions are necessary.
By oxidative decarboxylation of pyruvic acid, lactic acid, malonic acid, and
acetone, two substances form: acetic acid and carbon dioxide. The gas can be
identified easily.
The discovered reactant-product relations can also be interpreted on the molec-
ular level, when the structural formulae of the reactant molecules are familiar (or
when they are being introduced with the help of spectroscopic methods or by other
assumptions). Substances, which belong to different families, can thus be connected
with the help of the dichromate reagent to a system of synthetic relations that end in
one shared center (acetic acid). This unexpected connection of substances can
support the coherency of the knowledge and the student's systematic thinking.
The interdisciplinary aspect is also very interesting: in biology lessons students
get to know the central role of the activated acetic acid (acetyl-coenzyme A) within
