Description of experiment
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Needed compounds:
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sodium borohydride : NaBH4
manganese (II) sulfate : MnSO4 . H2O
Class:
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elem=Mn
precipitation
Summary:
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Manganese (II) is not reduced to the metal, it forms a white precipitate
with borohydride, which remains white for a long time. This precipitate
does not turn brown, as manganese (II) precipitates normally do in
alkaline environments.
Description:
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Add a solution of NaBH4 to a solution of manganese sulfate: Formation of a
white flocculent precipitate. The precipitate does not turn brown.
The reason that the precipitate does not turn brown is the excess amount
of borohydride in the solution.
Wait many hours: The precipitate has turned brown. The borohydride was
oxidized and oxygen then could oxidize the precipitate.