Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrogen peroxide : H2O2
sodium chlorate : NaClO3
sulphuric acid : H2SO4
hydrochloric acid : HCl
p-aminophenol HCl : NH2 C6H4 OH . HCl
Class:
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elem=C,Cl
redox
Summary:
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P-aminophenol, when oxidized, forms a deeply colored compound. The color
of this compound is deep blue/purple, but the environment and the used
oxidizer have some influence on the color of the liquid as a whole (other
compounds may make the color less pure).
Description:
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Sequence 1:
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Add some p-aminophenol HCl to hydrochloric acid (appr. 10% by weight): The
solid dissolves, the liquid becomes slightly colorized (a very pale pink/brown
color).
Add an excess amount of NaClO3: The liquid becomes dark pink/brown when the
sodium chlorate is dissolved. After some time, the color shifts towards
purple. After appr. 10 minutes, the liquid has become dark brown/purple.
At this point, the liquid is odourless.
After 4 hours (kept at appr. 20 C), the liquid has turned yellow and it still
is clear. Now there is a strong choking smell of chlorine above the liquid (in
fact, the entire room has a noticeable smell of chlorine).
Sequence 2:
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Add some p-aminophenol HCl to dilute sulphuric acid (appr. 10% by weight): The
solid dissolves, the liquid becomes slightly colorized (a very pale pink/brown
color).
Add an excess amount of NaClO3: The liquid slowly becomes blue/purple (indigo).
The reaction is much slower, than when hydrochloric acid is used of similar
concentration and the color also differs (more blue instead of brown). After
appr. 15 minutes, the liquid has a beautiful deep indigo color.
Heat the liquid to appr. 60 C: The color of the liquid further intensifies,
but it remains deep blue/indigo.
Sequence 3:
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Add some p-aminophenol HCl to dilute sulphuric acid (appr. 10% by weight): The
solid dissolves, the liquid becomes slightly colorized (a very pale pink/brown
color).
Add a large excess amount of H2O2 (3%): The liquid hardly changes. After 10
minutes at 20 C the liquid just has becomes a little darker pink/brown.
Heat to appr. 60 C: The liquid turns dark red/brown. Appr. 1.5 cm of the
liquid is completely opaque. Slow evolution of a gas (probable oxygen, due to
decomposition of H2O2) is observed. The liquid also becomes a little turbid.
After two days, both liquids of sequence 2 and sequence 3 are dark red and
a black solid has precipitated. The liquid of sequence 2 is a little bit
purplish, while the liquid of sequence 3 has no purplish hue.
When the liquids are shaken, then the black precipitate floats around in the
liquids as dark flakes.