Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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vanadium pentoxide : V2O5
sulphuric acid : H2SO4
sodium chlorate : NaClO3
hydroquinone : HO C6H4 OH
Class:
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elem=C,V
redox
Summary:
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Hydroquinone is oxidized by chlorate, but this reactions proceeds slowly.
When vanadium pentoxide is added in small quantities, then the reaction
proceeds much faster. The vanadium pentoxide acts as a catalyzer.
Description:
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Dissolve some hydroquinone in dilute H2SO4 (appr. 2% by weight) and add some
solid sodium chlorate: The solid quickly dissolves. The liquid remains
colorless. Even after a few minutes there is no clear change of the liquid.
Add a minute quantity of vanadium pentoxide: Quickly, the liquid turns yellow/
brown and a typical smell is produced. When the liquid is shaken continuously,
then the following sequence of colors occurs:
- colorless
- yellow/brown
- dark yellow/brown
- liquid becomes turbid
- formation of dark green crystals, liquid almost black
- liquid becomes lighter again (dark green, crystals disappear again)
- green/yellow, liquid almost clear
- intense yellow, clear liquid
- formation of bright yellow crystals in liquid
The entire reaction takes approximately 30 minutes, when the liquid is kept
hand-warm.
The dark green crystals are a coordination compound between hydroquinone
and quinone (quinhydrone), the yellow compound at the end of the experiment
is quinone. This has a pungent smell.