Description of experiment
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Needed compounds:
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hydrogen peroxide : H2O2
potassium ferrocyanide : K4 [Fe(CN)6] . 3H2O
sulphuric acid : H2SO4
zinc oxide : ZnO
Class:
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elem=Zn,Fe
precipitation
redox
Summary:
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Zinc (II) gives a white precipitate with ferrocyanide. This precipitate
becomes pale yellow, when treated with hydrogen peroxide (at least, when
in acidic environment).
Description:
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Add some solid zinc oxide to dilute H2SO4 (1 mol/l): The zinc oxide dissolves
and the resulting liquid is clear and colorless.
Add a small amount of solid potassium ferrocyanide: The solid dissolves, but
while it dissolves, an off-white precipitate is formed.
Heat the liquid with the precipitate to almost 100 C: No clear visible
changes. The precipitate looks a little bit more powder-like.
Add some H2O2 (appr. 6% by weight) to the still warm liquid: The precipitate
slowly turns yellow. It finally becomes pale yellow.