Description of experiment
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Needed compounds:
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cuprous iodide : CuI
Class:
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elem=I,Cu
Summary:
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Copper(I) iodide darkens on heating, but at the same time it decomposes, giving
deep purple iodine vapor.
Description:
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Put a spatula full of copper(I) iodide in a clean and dry test tube and heat
the test tube in the flame of a propane torch: The copper(I) iodide darkens
to a red/purple color. At the same time, vapors of iodine are released and the
material also melts. On stronger heating, quite a lot of iodine vapor is
produced and the liquid becomes black.
Allow the material to cool down and then add concentrated nitric acid: The
material cools down to a black mass. When the concentrated acid (53% by weight)
is added, then hardly any reaction occurs.
Heat the test tube with the black material and the acid: A fairly vigorous
reaction starts and a lot of brown gas is produced. Also iodine vapor is
produced, making the color of the gas mix appear more red instead of brown.
At colder parts of the glass, a lot of iodine crystals are deposited.
Keep on heating: At a certain point in time, the production of brown vapors
stops and then the test tube is filled with a deep blue liquid, with a lot of
dark purple iodine vapor above it.