Description of experiment
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Needed compounds:
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hydrochloric acid : HCl
catechol : C6H4 (OH)2
hydrogen peroxide : H2O2
cobalt chloride : CoCl2.6H2O
Class:
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elem=Co
coordination
redox
Summary:
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Cobalt (II) gives a coordination complex with catechol (or is this due
to formation of a cobalt (III) complex with catechol????).
Description:
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Add a single crystal of cobalt chloride to a solution of catechol in water:
The crystal dissolves and the liquid becomes pale pink. After a few minutes,
the color has changed to dark moss-green.
Add a few drops of H2O2 (3% solution): The liquid becomes intense dark green.
After appr. 10 minutes the liquid has become turbid. At that time it still
is dark green, but it looks much more grey than the fresh liquid, just after
addition of the H2O2.
Due to the intensity of the color and the turbidity of the liquid, it is not
easy to observe the real color of the liquid.
When the glass is cleaned, then a dark green layer sticks to the glass, which
cannot easily be removed with water. When some dilute HCl (10% by weight) is
added, then the glass can be cleaned easily and the color of the liquid,
used for rinsing the glass becomes pink (not a bright pink, but 'dirty' pink).