Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrochloric acid : HCl
manganese (IV) oxide : MnO2
hydrogen peroxide : H2O2
catechol : C6H4 (OH)2
nickel sulfate : NiSO4 . 6H2O
Class:
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elem=Ni
coordination
redox
Summary:
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Catechol appears to react with nickel (II), giving a coordination complex.
It is unclear, whether this is due to catechol itself or due to an
oxidation product, caused by oxidation by oxygen from air.
Description:
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Add a solution of nickel sulfate to a solution of catechol in water: At first
glance no reaction occurs. The resulting liquid is pale green. After a few
minutes, however, the liquid has turned much darker green. At the surface the
liquid is darker than at other places. The dark compound at the surface hence
apparently is the result of oxidation by air, followed by a coordination
reaction with the nickel (II) in the solution.
Add some H2O2 (3% solution) and let stand for a while: No visible changes in
the liquid. At the surface, the liquid again is darker than below the surface.
Apparently oxygen from the air does react, while H2O2 does not react. Another
possibility (although less expected) is that CO2 from the air causes the
dark color at the liquid's surface.
Add a little amount of MnO2 and shake: No clear bubbling and fizzling, which
normally is expected, when MnO2 is added to a solution, contain H2O2. When
the MnO2 has settled at the bottom, the liquid is dark green and almost
opaque.
Add some HCl (10% by weight): The liquid immediately turns brown.