Description of experiment
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Needed compounds:
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phenolphtalein : C (C6H4OH)2 C6H4 COO
hydrogen peroxide : H2O2
potassium ferrocyanide : K4 [Fe(CN)6] . 3H2O
Class:
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elem=Fe
redox
Summary:
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Ferrocyanide can be oxidized by hydrogen peroxide easily. This redox
reaction makes the liquid alkaline: H2O2 + 2e --> 2OH-
Description:
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Dissolve some potassium ferrocyanide in water and boil gently for a while:
No clearly visble changes. Perhaps the liquid becomes slightly more yellow,
but after some time of boiling it still is almost colorless.
Add some hydrogen peroxide (3% by weight) to the still warm liquid: The
liquid becomes yellow, like a solution of potassium ferricyanide. There
also is evolution of a gas (probably oxygen, from decomposing hydrogen
peroxide).
Add a few drops of phenolphtalein indicator: The liquid becomes red, hence
the liquid has become alkaline.