.
Sulfuric
acid is very corrosive, Chromium compounds are toxic.
Experiment
for a chemistry teacher. Use a tray. Do not forget goggles!
<--- The photos were done using potassium dichromate in earlier times
when the
high cancinogen potential
was not yet known.
Now the use of potassium dichromate for chemistry experiments is forbidden.
So potassium dichromate has to be replaced by potassium
permanganate.
An indirect
redox reaction of alcohol with permanganate/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 permanganate solution. Add 1 drop
of sulfuric acid and mix.
Observation
The
pink colour of permanganate disappears, 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, permanganate
ions being the electron acceptors. Alcohol
is oxidised leaving aldehyde, permanganate is reduced to manganese ions: