Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrogen peroxide : H2O2
ferrous sulfate : FeSO4 . 7H2O
hydrochloric acid : HCl
ferric chloride : FeCl3 . 6H2O
hydroquinone : HO C6H4 OH
pyrogallol : C6H3 (OH)3
metol : (CH3 NH C6H4 OH)2 . H2SO4
Class:
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elem=C
redox
Summary:
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The coordination complexes formed by iron-salts and phenol-like photographic
developers show very typical reactions with hydrogen peroxide. Many times
these reactions result in oxidation products which are not dark colored,
as opposed for oxidation by atmospheric oxygen.
Description:
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Sequence 1:
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Add an excess amount of H2O2 (3% solution) to a solution, containing metol
and ferric chloride, acidified with some hydrochloric acid: The yellow/brown
liquid turns dark red/brown, almost black. After one minute, however, the
liquid has turned much lighter again. Finally the liquid is orange/brown.
Sequence 2:
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Add a few drops of H2O2 (3%) to a solution, containing ferrous sulfate and
metol: The liquid turns intense purple/brown, almost black. After a few minutes
of standing the liquid has turned dark brown/black.
Add an excess amount of H2O2 (3%): Liquid becomes much lighter within appr.
10 seconds. The final color of the liquid is yellow/brown and the liquid is
slightly turbid.
Sequence 3:
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Add an excess amount of H2O2 (3%) to a dark brown solution, containing
slightly acidified ferric chloride and pyrogallol: Immediately, the color
of the liquid becomes much lighter (yellow/brown). The liquid remains
clear. When the liquid is shaken, little bubbles of a gas are evolved
(probably this gas is oxygen).
Sequence 4:
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Add an excess amount of H2O2 (3%) to a dark blue solution, containing
ferrous sulfate and pyrogallol: The liquid first turns dark brown and then
it becomes much lighter (this takes just a few seconds). The final color is
yellow/brown.
Sequence 5:
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Add some H2O2 (3%) to a solution, containing ferrous sulfate and hydroquinone:
The liquid turn dark brown/black and becomes turbid.
Sequence 6:
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Add some H2O2 (3%) to a solution of slightly acidified ferric chloride and
hydroquinone: The liquid turns dark brown. After some time, the liquid slowly
becomes lighter. When the liquid is shaken, bubbles of gas (probably oxygen)
are evolved. The final color is fairly intense brown/orange.