Description of experiment
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Needed compounds:
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sodium dithionite : Na2S2O4 . 2H2O
hydrochloric acid : HCl
ammonia : NH3
copper sulfate penta hydrate : CuSO4 . 5H2O
Class:
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elem=Cu
coordination
redox
Summary:
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When tetraammine-copper (II) is reduced by dithionite in excess ammonia,
then a colorless copper (I) complex is formed, which remains dissolved.
Description:
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Dissolve some copper sulfate in excess ammonia (5% by weight): The liquid
becomes deep blue and clear.
Add an excess amount of sodium dithionite (relative to the amount of copper
sulfate): The solid dissolves and the liquid becomes colorless and clear.
At the surface of the liquid a thin deep blue layer is formed, due to
oxidation by air. When the liquid is shaken, it becomes colorless again
(due to excess amount of dithionite).
Add an excess amount of HCl (10% by weight): A dark reddish brown precipitate
is formed in the liquid. Above the liquid some smoke is formed (due to
combination of gaseous NH3 and HCl).