Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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sodium hydroxide : NaOH
sulphuric acid : H2SO4
pyrogallol : C6H3 (OH)3
chlorine : Cl2
Class:
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elem=C,Cl
redox
Summary:
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Pyrogallol reacts with chlorine, forming an orange/red compound. When excess
chlorine is used, this compound is further oxidized to an almost colorless
compound.
Description:
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Prepare some chlorine gas (e.g. by adding excess hydrochloric acid to some
bleach) and bubble into a glass bottle. Mixing some air with the chorine gas
is of no concern, it does not need to be pure. Keep in the bottle, without
much liquid in it (some acidic or neutral liquid is of no concern).
Dissolve some pyrogallol in dilute sulphuric acid (a few percent by weight):
A colorless liquid is obtained.
Carefully pour the acidic solution of pyrogallol in the bottle, containing
chlorine gas: As soon as the liquid comes in contact with the chlorine gas,
it becomes orange/red. When the bottle is capped and shaken, with the
liquid and the chlorine gas in it, then the liquid remains orange/red, but
from a certain point, it quickly becomes lighter again. There was an excess
amount of chlorine and this further oxidized the orange/red compound to
a (almost) colorless compound. Finally, the liquid is pale green (due to
the compound or due to some dissolved chlorine?). The gas mixture above the
liquid still is green, due to excess chlorine gas, which did not react.
Add an excess amount of a solution of NaOH (such that the acid is neutralized
and all chlorine is absorbed): The liquid becomes orange/red again and is
strongly alkaline. There is no green gas in the gas mixture anymore and no
smell of chlorine can be observed anymore.