Description of experiment
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Needed compounds:
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potassium hydroxide : KOH
potassium dichromate : K2Cr2O7
hydrogen peroxide : H2O2
Class:
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elem=Cr
redox
coordination
Summary:
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From ice cold strongly alkaline solutions of potassium chromate, one can
create peroxochromate by adding hydrogen peroxide carefully.
Description:
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Prepare a concentrated solution of potassium dichromate with an excess amount
of potassium hydroxide. The liquid must be yellow and contain a large excess
amount of hydroxide. Let this liquid cool down in a refrigerator.
Add some ice cold H2O2 (27%) to the ice cold potassium chromate/hydroxide
solution and mix carefully: The liquid turns dark red/brown and some gas
(oxygen) is evolved. The liquid becomes slightly warmer during this reaction.
After a few hours of standing in the cold, a large amount of crystals of a
brown solid are deposited at the bottom. These crystals consist of potassium
tetraperoxochromate (V), K3CrO8.