Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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ammonia : NH3
hydrogen peroxide : H2O2
potassium dichromate : K2Cr2O7
sulphuric acid : H2SO4
aniline : C6H5NH2
Class:
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elem=C,N,Cr
organic
redox
Summary:
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Aniline gives colored compounds with chromium. The colors are remarkably
intense.
Description:
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Prepare a solution of anilinium sulfate in excess of sulphuric acid by adding
some aniline to dilute sulphuric acid. If the solution is not entirely
colorless, then some activated charcoal can be added and shaken with the
liquid. After a day of standing a clean and colorless solution of anilinium
sulfate is obtained.
Add an excess amount of 3% H2O2 to some of the acidic solution of anilinium
sulfate: The liquid becomes light brown. No bubbles of oxygen can be observed.
Mix the liquid with a lot of water: An (almost) colorless liquid is obtained.
Again, no bubbles of oxygen can be observed.
Add a few crystals of potassium dichromate: The liquid becomes deep blue and
oxygen gas is produced. The deep blue color is due to formation of CrO5. After
a while, the deep blue color disappears and the liquid first becomes purple and
finally it becomes beautifully red, like red wine. The transient purple color
probably is due to a mix of the blue of CrO5 and the final deep red color. The
liquid also has a very strange and unpleasant odor. The deep red liquid remains
clear. It also seems to be irritating
Add an excess amount of 5% NH3: The liquid becomes yellow/brown and somewhat
turbid.
Remarks:
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The colors in this experiment are very intense. The nature of the deep red
compound is not known (at least not to me). The reaction with aniline and
dichromate in the presence of H2O2 is quite different from the reaction without
H2O2. Without H2O2 a deep blue/black precipitate is formed and on addition of
ammonia, the liquid becomes indigo. A more thorough description is that
experiment is available as well.