Description of experiment
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Needed compounds:
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ferric chloride : FeCl3 . 6H2O
sodium thiosulfate : Na2S2O3 . 5H2O
potassium ferricyanide : K3 [Fe(CN)6]
Class:
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elem=Fe
precipitation
redox
Summary:
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Thiosulfate is capable of reducing ferricyanide, but it is not capable
of reducing ferroferricyanide (Prussian blue).
Description:
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Add a solution of potassium ferricyanide to a ilarge excess amount of a
solution of sodium thiosulfate: The resulting liquid remains yellow, just
as the original solution of potassium ferricyanide.
Wait for almost one day: The liquid has turned almost colorless and has
become slightly turbid (just visible, faint milkyness). It appears that
the yellow ferricyanide in solution has been reduced to almost colorless
ferrocyanide.
Add a little amount of ferric chloride, dissolved in water: The liquid
turns dark blue and turbid at once.
Wait for a few days: The dark blue compound has settled on the bottom of
the glass container. The liquid above the blue compound is clear and
almost colorless. When shaking, the liquid becomes dark blue again. The dark
blue compound is not reduced by the thiosulfate. Apparently thiosulfate does
not reduce the iron (III) in the dark blue compound.