Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrochloric acid : HCl
oxalic acid : HOOC COOH . 2H2O
sodium hydroxide : NaOH
ferric chloride : FeCl3 . 6H2O
ferrous sulfate : FeSO4 . 7H2O
Class:
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elem=Fe
coordination
Summary:
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Ferrous ions give a yellow coordination complex with oxalate. The normal
color of ferrous ions is pale green. Ferric ions give a green coordination
complex with oxalate. The normal color of ferric ions is yellow/brown.
The ferric complex is only formed if the environment is not too acidic.
Description:
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Sequence 1
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Add solid ferrous sulfate to a solution of oxalic acid: The solid dissolves,
the liquid becomes intense yellow and clear. When more and more of the solid
dissolves, the liquid becomes turbid. After some time a yellow precipitate
is formed. The liquid above the precipitate becomes clear and pale yellow
(almost without color).
Sequence 2
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Add a solution of ferric chloride (a little acidified with HCl in order to
make it clear) to a solution of oxalic acid: The liquid becomes yellow.
No coordination complex (or just a little bit) is formed. This is probably
due to the fact that the ferric chloride was a little acidified.
Add an excess amount of a solution of NaOH: Formation of a brown precipitate.
Add a solution of oxalic acid: The precipitate dissolves and the liquid
becomes green. The color is a very bright green/yellow.