Description of experiment
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Needed compounds:
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ferric chloride : FeCl3 . 6H2O
sodium hydroxide : NaOH
catechol : C6H4 (OH)2
hydrochloric acid : HCl
copper sulfate penta hydrate : CuSO4 . 5H2O
Class:
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elem=Cu,Fe
coordination
Summary:
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Copper gives a coordination complex with catechol, but only in alkaline
environments. This complex is easily oxidized by oxygen from air. Iron
also forms a complex in acidic media, probably by a combined red/coordination
reaction.
Description:
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Add a solution of copper sulfate to a solution of catechol in HCl (3% by
weight): The liquid becomes pale blue.
Add an excess amount of a solution of NaOH: The liquid turns yellow/brown
and remains clear. At the surface of the liquid a dark compound is formed
(by oxidation from air). Slowly, the whole liquid turns darker. After one
hour of standing the liquid has become dark brown/yellow.
Add a solution of ferric chloride to the pale blue liquid: Initially the
liquid becomes yellow, but quickly it turns darker. Finally the liquid is
dark brown and a little turbid. When the liquid is strongly diluted with
water it becomes grey.