Description of experiment
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Needed compounds:
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potassium ferrocyanide : K4 [Fe(CN)6] . 3H2O
ferrous sulfate : FeSO4 . 7H2O
Class:
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elem=Fe
precipitation
coordination
Summary:
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Reaction between ferrous-ion and hexacyanoferrate (II) ion.
Description:
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Add a fresh solution of ferrous sulfate to a solution of K4[Fe(CN)6].3H2O:
A pale blue precipitate appears, which makes the liquid look like a pale
blue milk.
Add an excess amount of sodium metabisulfite: The solid dissolves in the
liquid. The liquid remains pale blue.
Remark: The pale blue color probably is due to the fact that a solution
of ferrous sulfate will always contains a slight amount of iron (III). This
reacts with the ferrocyanide to a blue compound. The excess amount of
metabisulfite is not capable of reducing the blue compound to a pure
iron (II) compound.