Description of experiment
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Needed compounds:
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vanadium pentoxide : V2O5
hydrogen peroxide : H2O2
sulphuric acid : H2SO4
hydroquinone : HO C6H4 OH
Class:
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elem=C,V
redox
Summary:
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Vanadium pentoxide catalyzes the oxidation of hydroquinone to quinone by
hydrogen peroxide.
Description:
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Add some solid hydroquinone to dilute H2SO4 (appr. 2 mol/l): Part of the solid
dissolves. The liquid becomes colorless and clear.
Add water, approximately the same volume as that of the dilute H2SO4: More of
the hydroquinone dissolves, liquid remains colorless.
Add some H2O2 (30% by weight), appr. one quarter of volume of the liquid
already available: No visible reaction. After waiting one minute there still
is no visible change.
Add a minute quantity of V2O5: The liquid becomes yellow/brown quickly. A while
later, it becomes red/brown and somewhat turbid. After approximately half an
hour a dark green solid has formed, consisting of many shiny crystals. There
is no clearly visible eveolution of a gas. The reaction does not proceed
particularly fast.
After one day, all little crystals have disappeared and an amorphous slurry
is floating in the liquid and on the surface of the liquid.
A few days later, all solid matter has disappeared. The liquid is clear and
orange/red/brown. It looks like a fairly concentrated solution of bromine
in water.
The liquid remains red/orange for many days and then suddenly within one day
it becomes much lighter yellow/brown.