Description of experiment
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Needed compounds:
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sodium hydroxide : NaOH
potassium permanganate : KMnO4
sulphuric acid : H2SO4
nickel sulfate : NiSO4 . 6H2O
Class:
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elem=Ni,Mn
precipitation
redox
Summary:
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Permanganate is not capable of oxidizing nickel (II) in an acidic
environment. In an alkaline environment it appears to be possible to
oxidize nickel (II) with permanganate.
Description:
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Dissolve some nickel sulfate in dilute sulfuric acid (appr. 10% by weight)
and add a minute amount of KMnO4: The solution turns purple/violet, due to
the strong color of [MnO4]-, the pale green color of the nickel (II) ions
is hidden by the intense color of the permanganate. The nickel (II) is not
oxidized by the permanganante.
Add an excess amount of concentrated NaOH-solution: A dark brown precipitate
is formed. It looks as if the [MnO4]- is reduced to MnO2. The precipitate
probably is a mixture of MnO2, Ni(OH)2 and an oxidation product of Ni(OH)2.