Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrochloric acid : HCl
manganese (II) sulfate : MnSO4 . H2O
copper sulfate penta hydrate : CuSO4 . 5H2O
sodium metaperiodate : NaIO4
Class:
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elem=Mn,Cu,I
coordination
redox
Summary:
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When copper ions are brought in contact with periodate, then a yellow/green
precipitate is formed. This precipitate very easily dissolves in hydrochloric
acid, giving chlorine gas and other products.
When the same is done with manganese(II) ions instead of copper ions, then a
brick-red precipitate is formed, which does not easily dissolve in hydrochloric
acid.
Description:
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Prepare a solution of sodium metaperiodate in test tube A.
Prepare a solution of manganese sulfate in test tube B.
Prepare a solution of copper(II) sulfate in test tube C.
Add some of liquid A to liquid B: A brick-red precipitate is formed. Formation
of the precipitate is not instantaneous.
Add some of liquid A to liquid C: A yellow/green precipitate is formed, almost
instantaneously.
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Add some hydrochloric acid (10% HCl by weight) to the mix of liquid A and
liquid B: No visible changes occur. Even after a minute or so, the precipitate
still is brick-red.
Heat the liquid with the acid and the brick-red precipitate: While this is
done, the color changes from brick-red to very dark brown, almost black. The
liquid remains turbid. Only after prolonged heating, the black material slowly
disappears and a strong smell of chlorine appears. Finally, the liquid is deep
yellow and clear.
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Add some hydrochloric acid (10% HCl by weight) to the mix of liquid A and
liquid C: The yellow/green precipitate quickly dissolves, while a gas is
evolved. This gas is chlorine. After a few tens of seconds all of the
precipitate is dissolved, there is no need to heat the liquid. Finally, the
liquid is yellow/green and clear.
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Remark: The complex of periodate and manganese is much more resistant to attack
by reducing acid like HCl. Probably the precipitated complex is less soluble,
or it is less easily oxidized.
Is the brick-red precipitate a compound of manganese(II) or is it a compound of
manganese(III). This cannot be deduced from this simple experiment. The black
material, formed on heating of the acidified precipitate most likely is hydrous
MnO2.