Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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ascorbic acid : C6H8O6
sulphuric acid : H2SO4
ammonia : NH3
vanadium pentoxide : V2O5
Class:
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elem=V,N
redox
acid/base
Summary:
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Vanadium pentoxide dissolves in ammonia and when heated a white solid is
formed, probably this is ammonium meta vanadate.
Description:
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Add some vanadium pentoxide to ammonia (appr. 5% by weight): The vanadium
pentoxide dissolves fairly easily without the need to heat the liquid. The
liquid becomes intense yellow and clear.
Heat for some time and boil: The liquid becomes lighter and lighter. Finally,
the liquid almost (but not completely) becomes colorless and there is no
more smell of ammonia. All the ammonia is driven off by boiling the liquid.
Let liquid stand for appr. 9 hours: The liquid now has becomes completely
clear and colorless. A small crust of off-white crystals have separated from
the liquid and have settled on the glass.
Sequence 1:
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Decant the liquid from the crystals and add some sulphuric acid to the
colorless liquid (which does not contain any crystals): The liquid becomes
yellow and clear.
Add some ascorbic acid to the yellow liquid: The liquid becomes blue almost
instantly, as the ascorbic acid dissolves.
Sequence 2:
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Add some water to the off-white crystals: The solid hardly dissolves.
Rinse the crystals well with some cold water and then add some sulphuric
acid (appr. 2 mol/l) to the wet crystals: The crystals become orange/red
at once, as soon as the acid touches them. The liquid becomes light yellow.
The crystals do not dissolve. After approximately 5 minutes, the crystals
have been transformed into a brown/red slurry, which does not dissolve.
Add some ascorbic acid: The ascorbic acid dissolves, the brown/red slurry
turns black and the liquid becomes blue and clear. Not all of the slurry
dissolves, even when some additional water is added some of the black stuff
remains.