Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrochloric acid : HCl
hydrogen peroxide : H2O2
sodium hydroxide : NaOH
tartaric acid : HOOC CHOH CHOH COOH
cobalt chloride : CoCl2.6H2O
Class:
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elem=Co
coordination
redox
Summary:
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Cobalt gives a green coordination complex with tartrates, when oxidized to
the +3 state.
Description:
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Add a solution of cobalt chloride to a solution of tartaric acid/NaOH: The
liquid remains pink (an excess amount of tartaric acid was used).
Add much more solid sodium hydroxide: Around the pieces of NaOH a blue
precipitate is formed (Co(OH)2). When the liquid is shaken, both the
precipitate and the NaOH dissolve. The liquid becomes grey and clear.
Add a little amount of H2O2 (3% by weight): Evolution of a gas, the liquid
turns moss-green.
Add much more H2O2 (3%): The liquid becomes brown/green, stronger evolution
of a gas.
Add an excess amount of HCl (10% by weight): Sudden strong evolution of
gas, strong foaming, liquid almost bubbles out of test tube. The liquid
turns pale yellow/green. The strong evolution of gas almost immediately
stops after its vigorous start. After the foam has collapsed again, a
clear pale yellow/green liquid remains.