Description of experiment
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Needed compounds:
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hydrochloric acid : HCl
sodium borohydride : NaBH4
cobalt sulfate : CoSO4.7H2O
Class:
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elem=Co
redox
Summary:
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Borohydride is capable of reducing cobalt (II) to the metallic state.
Description:
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Add a solution of sodium borohyride to a solution of cobalt sulfate: A lot
of gas is produced and a finely divided black precipitate is formed. On
the glass, metallic shiny stains can be observed.
Add a lot of water and let the precipitate settle at the bottom and decant
most of the water from the test tube. Next add some concentrated HCl, such
that the final concentration becomes approximately 10% by weight: The
black precipitate slowly dissolves and the liquid becomes clear and deep
blue/purple.
Add a lot of water: The liquid becomes pink.