Description of experiment
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Needed compounds:
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sulphur : S8
aluminum : Al
potassium permanganate : KMnO4
Class:
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elem=Al,S,Mn
redox
Summary:
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A mix of aluminium powder and potassium permanganate is hard to ignite. When a
small amount of sulphur is added, then the mix is easily ignited, and a very
bright and fast burning flash is produced.
Description:
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Mix approximately 80 mg of finely powdered potassium permanganate with 20 mg of
powdered aluminium (400 mesh) and take out a small part of this (10 mg or so):
The mix is not easily ignited. The flame of an alcohol burner is not capable of
igniting the mix.
Add a small amount of sulphur (10 mg or so) and carefully mix this with the
remaining mix. Take some of this new mix (again 10 mg or so) and keep this in
the flame of an alcohol burner: The mix is easily ignited and gives a very
bright white flash. White smoke is produced, and many small black particles are
sprewn around.
Take a somewhat larger amount (50 mg or so) and light again: The flash is
accompanied with a fairly strong hissing/whoosh sound. Again, the flash is
increadibly bright and very fast.
Rinse the black particles with water: Many particles leave a purple trail,
these are unreacted potassium permanganate. But there also are particles which
leave a deep green train when rinsed with water. This is decomposed potassium
permanganate, which has not reacted with the aluminium. The decomposotion is
due to the heat of the reaction, the products are K2MnO4 (giving the green
color on addition of water), MnO2 and O2.
Remark: The sulphur really is necessary to make ignition of the mix much
easier. Probably this is because it is in more intimate contact with the KMnO4
when heated initially, and the heat of that reaction in turn is sufficient to
ignite the Al/KMnO4 mix.