Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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chrome alum : KCr(SO4)2 . 12H2O
sodium hydroxide : NaOH
ferric chloride : FeCl3 . 6H2O
sodium persulfate : Na2S2O8
sodium sulfite : Na2SO3
pyrogallol : C6H3 (OH)3
Class:
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elem=C
coordination
redox
Summary:
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Pyrogallol gives rise to many colored products on oxidation and coordination.
More investigation is needed in order to get more insight in all these
colors and the conditions under which they are formed.
Description:
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Add some pyrogallol and an excess amount of sodium sulfite to luke-warm water:
The solids dissolve. First the liquid becomes pale pink, but quickly it
becomes colorless. This colorless liquid is called SULFITE-PYRO.
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Add a solution of ferric chloride to some SULFITE-PYRO: The liquid turns dark
brown. On strong dilution, the color shifts to blue/grey.
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Add an excess amount of sodium persulfate to SULFITE-PYRO: The solid dissolves
and the liquid turns pink/orange. This color is fairly intense.
Add a few pieces of NaOH: The liquid turns much darker for a short time. After
this transient it becomes pink again. After a longer period of standing the
color of the liquid becomes pale yellow.
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Add some solid NaOH and solid chrome alum to SULFITE-PYRO: Both solids
dissolve. First, the liquid turns green, but on prolonged shaking the color
shifts towards dark brown/sepia.
Pour out on a white ceramic tile: The liquid appears sepia (a layer of 1 - 2
mm) on the white ceramic. After approximately half a minute, however, the
color has shifted to a bright orange. Apparently the liquid absorbs oxygen
from the air and this causes a shift from sepia to intense orange.