Description of experiment
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Needed compounds:
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potassium tetrachloro iodate (III) : KICl4
magnesium : Mg
Class:
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elem=Mg,Cl,I
redox
Summary:
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Magnesium and potassium tetrachloro iodide do not react when dry, but when a
drop of water is added, then a violent reaction starts, with production of
purple clouds of iodine.
Description:
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Mix some excess amount of magnesium powder and finely ground potassium
tetrachloroiodide with each other: No reaction occurs.
Add a small drop of water: Where the water reaches the mix, a violent reaction
starts with emission of purple vapor of iodine. The reaction, however is not
self-sustained. Dry powder, adjacent to the wet mix, does not react. Only when
that powder is made wet, it also reacts violently.
The remarkable thing is that iodine is released in this reaction. No brown
iodine chloride is produces. Apparently, the chlorine in the compound is so
much the more reactive species, that iodine is allowed to escape and not react
with magnesium.