Description of experiment
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Needed compounds:
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sodium hydroxide : NaOH
sodium persulfate : Na2S2O8
copper sulfate penta hydrate : CuSO4 . 5H2O
pyrogallol : C6H3 (OH)3
Class:
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elem=C,Cu
redox
Summary:
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Copper (II) apparently catalyses the oxidation of pyrogallol by oxygen from
the air.
Description:
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Add some solid copper sulfate to a solution of pyrogallol: The solid dissolves
and the liquid turns brown and slightly turbid.
Add some solid sodium persulfate: The solid dissolves, the liquid turns clear
and the color becomes less intense. The color is red/brown.
Add some solid NaOH: At the pieces of NaOH a black, very dark compound is
formed. When the liquid is shaken, it becomes intense dark red/brown, almost
black. It is not possible to see, whether the liquid is still clear or whether
a dark precipitate is present in the liquid.