Description of experiment
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Needed compounds:
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sulphuric acid : H2SO4
zinc oxide : ZnO
potassium iodide : KI
potassium ferricyanide : K3 [Fe(CN)6]
Class:
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elem=Fe,I
precipitation
redox
Summary:
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Ferricyanide is capable of oxidizing iodide to iodine, even in neutral
environments. The reaction, however does not appear to go to completion.
Description:
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Add some solid K3Fe(CN)6 to a concentrated solution of KI: The solid dissolves,
the liquid turns dark red/brown.
Add some acidic solution of ZnSO4 (prepared by dissolving ZnO in dilute
sulphuric acid): Formation of a brown/orange precipitate, the color of the
liquid becomes less intense.
Remark: It appears that the addition of the zinc ions takes away ferri-
cyanide ions, which causes the equlilibrium between iodine/ferrocyanide and
iodide/ferricyanide to be shifted to the iodide/ferricyanide-side. The
ferricyanide is taken away by precipitation with zinc, yielding a brownish
orange precipitate.