Description of experiment
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Needed compounds:
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hydrogen peroxide : H2O2
hydrochloric acid : HCl
sodium thiosulfate : Na2S2O3 . 5H2O
potassium ferricyanide : K3 [Fe(CN)6]
ferric chloride : FeCl3 . 6H2O
Class:
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elem=Fe
precipitation
coordination
redox
Summary:
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Ferricyanide gives a dark brown coordination complex with ferric ions. This
complex is soluble in water. It is easily transformed to the much more
stable, dark blue and insoluble ferroferricyanide.
Description:
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Add a solution of slightly acidified ferric chloride (acidified with a few
drops of HCl) to a solution of potassium ferricyanide: The liquid turns dark
brown. It stays clear.
Add some solid Na2S2O3.5H2O to the dark brown liquid: The solid dissolves.
The liquid becomes dark blue and a dark blue precipitate is formed. A
transient color (dark green) can be observed, before the liquid becomes
dark blue. This transient color is visible for a few seconds.
Add some hydrogen peroxide (3% by weight) and some HCl (10% by weight) to
the dark brown liquid: The liquid slowly turns darker and changes color
from brown, through dark green to dark blue. Although the dark brown
complex only contains iron (III), it appears to be possible to turn into
iron (II) partly, even in the presence of an oxidizing agent as H2O2.
(Or acts the H2O2 as a reductor in this case????)