Description of experiment
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Needed compounds:
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hydrochloric acid : HCl
sodium hydroxide : NaOH
ammonia : NH3
vanadyl sulfate : VOSO4.5H2O
Class:
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elem=V
coordination
Summary:
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Vanadyl (vanadium (IV)) does not give a coordination complex with ammonia.
It does not dissolve in ammonia. With stronger bases, a brown vanadate (IV)
compound dissolves (a poly-vanadate (IV) compound??).
Description:
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Add an excess amount of ammonia (5% by weight) to a slightly acidic solution
of vanadyl sulfate: Formation of a brown precipitate. This precipitate
does not dissolve lateron.
Add much more ammonia: No further changes.
Add an excess amount of NaOH: The solid dissolves, the liquid becomes clear
again and becomes intense red/brown. Some dark particles remain sticking to
the glass and these do not dissolve. So only the smaller particles dissolve,
the larger pieces do not dissolve completely.
Add an excess amount of hydrochloric acid (appr. 10% by weight): The liquid
becomes blue again. The dark pieces of precipitate now do dissolve, but this
takes a few minutes.