Description of experiment
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Needed compounds:
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sodium persulfate : Na2S2O8
sodium hydroxide : NaOH
ascorbic acid : C6H8O6
nickel sulfate : NiSO4 . 6H2O
Class:
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elem=Ni
redox
coordination
Summary:
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Nickel (II) does not form a coordination complex with ascorbic acid, not
in neutral or slightly acidic environments, nor in alkaline environments.
Description:
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Add a solution of nickel sulfate to a solution of ascorbic acid: Liquid
becomes pale green, no visible reaction.
Add an excess amount of a solution of NaOH: Formation of a pale green
precipitate.
Add some solid Na2S2O8: The precipitate does not turn dark brown/black.
Without the ascorbic acid this would happen, hence one can conclude that
the ascorbic acid reduces the persulfate and no persulfate is left for
oxidizing the Ni(II) precipitate.