Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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sodium dithionite : Na2S2O4 . 2H2O
ammonia : NH3
potassium iodide : KI
copper sulfate penta hydrate : CuSO4 . 5H2O
Class:
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elem=Cu,I
coordination
redox
Summary:
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Copper (I) iodide dissolves in dilute ammonia, resulting in a colorless
liquid. Copper (I) builds a coordination complex with ammonia. This
complex is oxidized by oxygen from the air exceedingly easily.
Description:
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Add a solution of potassium iodide to a solution of copper sulfate: The
liquid turns dark brown and a white precipitate is formed.
Rinse several times with tap-water and keep the precipitate: A pale grey
solid is obtained, which does not dissolve in water. This is copper (I)
iodide.
Add some ammonia (5% by weight) to the solid copper (I) iodide: The solid
dissolves and the liquid becomes clear and colorless. After approximately
half a minute, the surface of the liquid is deep blue, the rest of the
liquid still is colorless. When the liquid is shaken, it becomes pale
blue.
Add a little amount of sodium dithionite: The solid dissolves and the liquid
becomes pale yellow (almost colorless).
Keep in contact with air: Everywhere, where the liquid is in contact with
air, it becomes deep blue quickly. When shaken, it turns pale yellow again
(the blue copper (II) complex is reduced by the dithionite to the colorless
copper (I) complex). After a few times of shaking, the liquid remains blue.
At that point all dithionite is oxidized and the liquid becomes more and
more blue, until it is deep blue.