Description of experiment
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Needed compounds:
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potassium persulfate : K2S2O8
nitric acid : HNO3
hydrochloric acid : HCl
sodium borohydride : NaBH4
nickel sulfate : NiSO4 . 6H2O
Class:
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elem=Ni
redox
Summary:
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Borohydride is capable of reducing nickel to the metallic state in
aqueous media.
Description:
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Add a solution of NaBH4 to a solution of nickel sulfate: Formation of a
black precipitate. One the glass, shiny metallic stains can be observed.
Besides this, a lot of gas is produced (H2).
Add a lot of water and let the precipitate settle at the bottom. Decant the
water and add concentrated HCl (appr. 30% by weight), such that the acid
concentrated becomes approximately 15% by weight: The black precipitate
does not dissolve.
Add a small amount of nitric acid (52% by weight): The precipitate still
does not dissolve. Even the metallic stains on the glass do not disappear.
Add some solid K2S2O8 and shake for a while: Only slowly and with the help
of some heating to appr. 60 C the metallic stain and the black precipitate
disappear. The liquid becomes blue again.