Description of experiment
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Needed compounds:
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sodium sulfide : Na2S . 3H2O
sodium metabisulfite : Na2S2O5
potassium permanganate : KMnO4
Class:
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elem=Mn,S
precipitation
redox
Summary:
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This experiment shows two things:
1) Permanganate can be reduced by metabisulfite, but the reduction does
not proceed instantaneously when no additional acid is used.
2) Manganese sulfide is a dirty pink substance (color of flesh).
Description:
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Add an excess amount of a solution of Na2S2O5 to a solution of KMnO4: The
liquid decolorizes. Complete decolorization takes appr. 30 seconds through
the following sequence purple --> red --> reddish brown --> yellow/brown -->
pale yellow --> colorless.
Add a solution of Na2S: At first glance nothing seems to happen, however,
after a few seconds the liquid becomes milky. A few more seconds later the
liquid becomes completely opaque and dirty pink. A strong smell of H2S can
be observed.