Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrochloric acid : HCl
potassium iodide : KI
cuprous iodide : CuI
Class:
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elem=I,Cl,Cu
coordination
Summary:
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Copper(I) iodide dissolves in a concentrated solution of potassium iodide.
In such a solution the complex ion CuI2(-) is formed. On dilution, this ion
decomposes and a precipitate of CuI is formed again.
Copper(I) iodide does not dissolve in hydrochloric acid, or just a small
amount dissolves.
Description:
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Sequence 1:
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Add a small amount of copper(I) iodide to a concentrated solution of potassium
iodide: Part of the copper(I) iodide dissolves. The solubility of copper(I)
iodide is not spectacular, but a noticeable amount of copper(I) iodide dissolves.
Allow the suspended copper(I) iodide to settle at the bottom and pour the
clear solution in a large amount of water: The liquid becomes turbid and white.
The complex, formed in the concentrated solution of potassium iodide falls
apart on dilution and copper(I) iodide precipitates.
Sequence 2:
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Add some copper(I) iodide to concentrated hydrochloric acid (30% by weight):
The solid becomes suspended in the acid, but it does not dissolve. On long
shaking with contact with air, the liquid becomes more and more yellow, but
the visible amount of copper(I) iodide does not change. Apparently, a very
small amount of copper(I) iodide is oxidized and iodine comes in solution,
together with some copper(II). Both give rise to a yellow color in the
concentrated acid.