Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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potassium ferricyanide : K3 [Fe(CN)6]
potassium ferrocyanide : K4 [Fe(CN)6] . 3H2O
sodium citrate : COONa CH2 COH(COONa) CH2 COONa
copper sulfate penta hydrate : CuSO4 . 5H2O
Class:
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elem=Cu,Fe
coordination
Summary:
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Copper (II) builds a complex with citrate ions. When treated with ferro
cyanide, this complex is destroyed, resulting in copper ferrocyanide.
When treated with ferricyanide, then it is not destroyed. Apparently
copper ferricyanide dissolves better in water, such that the complex
with citrate can remain in solution.
Description:
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Sequence 1
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Add a solution of copper sulfate to a solution of sodium citrate: The
resulting liquid is intense blue, much more intense than a solution,
containing ordinary hydrated copper (II).
Add a solution of potassium ferrocyanide to the intense blue liquid: The
liquid becomes turbid and dark purple/brown. A very finely divided
precipitate is formed. When the precipitate is spread on a piece of
white paper, then it has a brown/red color, with a pink shade. This
is used in photography as a copper toner.
Add a solution of potassium ferricyanide to the intense blue liquid: The
liquid becomes bright green and remains clear.
Sequence 2
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Add a solution of copper sulfate to a solution of potassium ferricyanide:
Formation of a dirty brown/green precipitate, which does not dissolve on
strong dilution.
Add a solution of sodium citrate: The precipitate dissolves, the liquid
becomes clear and has a bright yellow/green color.