Description of experiment
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Needed compounds:
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ethanol : CH3CH2OH
sulphuric acid : H2SO4
sodium orthovanadate : Na3VO4
Class:
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elem=V
redox
Summary:
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Vanadium in oxidation state +5 is capable of oxidizing ethanol in acidic
solution, but this reaction is very very slow.
Description:
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Add some solid sodium orthovanadate to dilute sulphuric acid (20% H2SO4 by
weight): The solid becomes covered by a dark red/brown layer, but on shaking
for several minutes it all dissolves and a bright yellow solution is obtained.
To this solution add some ethanol and shake: The ethanol mixes with the liquid
and the liquid remains clear and bright yellow.
Heat the liquid until it starts boiling: The liquid remains bright yellow. Even
after minutes of boiling it remains yellow.
Put the hot liquid aside: After half an hour there is a faint shift of color.
Instead of yellow, the liquid now looks lime yellow/green. The liquid has
cooled down in the meantime.
Wait another few days: After one day, the liquid still looks lime green, but it
has shifted somewhat more towards green. After three days of waiting, the
liquid looks somewhere halfway between green and yellow. After a week the
liquid looks green.
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Vanadium in oxidation state +5 has a bright yellow color in the acidic solution
and vanadium in oxidation state +4 is bright blue. The greenish colors are due
to mixing of yellow and blue and while more of the vanadium is converted to
oxidation state +4 the color more and more goes towards blue. But even after a
week only part of the vanadium is reduced to oxidation state +4.