Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrochloric acid : HCl
hydrogen peroxide : H2O2
anhydrous chromic acid : CrO3
Class:
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elem=Cr
redox
Summary:
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Chromic acid reacts with hydrogen peroxide under formation of a dark blue
compound. When more hydrogen peroxide is added, then apparently the pH of
the liquid becomes too high and other almost black compounds are formed,
which quickly decompose.
Description:
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Add some H2O2 (appr. 30%) to a solution of CrO3 in water: The first little
amount of H2O2 causes a blue coloration, when more H2O2 is added, then the
liquid turns very dark (almost black) and starts foaming, such that part of
the liquid foams out of the test tube.
Dilute the remaining part of the liquid very strongly with water: The liquid
is brown, when viewed under white TL-light, it appears brown/red/purple, hard
to describe, when viewed under tungsten light.
Add some HCl (appr. 10% by weight): Liquid becomes deep blue and remains like
this for a fairly long time. Apparently the deep blue compound is more stable
at low concentrations.