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org11 Aldehyde by direct oxidation of alcohol by dichromate/sulfuric acid
Sulfuric
acid is very corrosive, Chromium compounds are toxic.
Experiment
for a chemistry teacher. Use a tray. Do not forget goggles!
An indirect
redox reaction of alcohol with dichromate/sulfuric acid was already
done to produce electricity in a Galvanic Cell.
Now you will mix the three
components in a small stoppered bottle. Now you can smell the volatile
product and test it by an indicator: "Alcoholus
dehydrogenatus"
= alcohol which was deprived from hydrogen = aldehyde.
* Mix 1 drop of methylated
spirit and 2 drops of diluted potassium dichromate solution. Add
1 drop of sulfuric acid and mix.
Observation
left photo:
The orange colour (dichromate ions left) disappears, a blueish colour of
chrome ions (right) can be seen, a smell characteristic for acetaldehyde
(ethanal) appears.
Right photo: Add
colourless solution of fuchsin sulfurous acid to a piece of tissue paper,
fix it in the vial by the stopper: The red colour indicates gaseous aldehyde.
Explanation:
Alcohol molecules are the electron donors
in this direct redox reaction, dichromate
ions being the electron acceptors.
Alcohol is oxidised leaving aldehyde, dichromate is reduced to chromium
ions: