Description of experiment
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Needed compounds:
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sodium chloride : NaCl
aluminum : Al
nitric acid : HNO3
cupric chloride dihydrate : CuCl2 . 2H2O
Class:
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elem=Cu,Cl,N,Al
coordination
redox
Summary:
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Copper (II) chloride dissolves in fairly concentrated nitric acid, but it does
not dissolve easily. Only a small amount can be dissolved. It dissolves with
a bright green/cyan color. Aluminum metal is not attacked by this solution.
Slight dilution does not make the liquid more active towards aluminum. When a
lot of sodium chloride is added, then the aluminum is attacked and it
dissolves.
Description:
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Add some solid copper (II) chloride dihydrate to nitric acid (52% HNO3 by
weight): Only a small part of the solid dissolves. The liquid becomes clear
and bright green/cyan.
Add a small piece of aluminum foil: The foil does not dissolve, it does not
change at all. It remains floating on the liquid.
Add some water (approximately the same volume as the nitric acid) carefully:
Two layers are formed, a colorless layer on top of the green layer. The border
between the two layers is not sharp. The piece of aluminum foil is floating
somewhere in the border between the nitric acid layer and the water-layer.
Shake well: The two layers of liquid mix with each other, the copper chloride
now dissolves completely. The liquid becomes green/cyan. The piece of aluminum
still is not attacked, although now a fairly large amount of copper chloride
is in solution. Apparently the nitric acid has a strong passivating effect on
the aluminum. The piece of aluminum sinks to the bottom.
Add a fairly large amount of NaCl: Most of the NaCl dissolves. The piece of
aluminum foil again starts floating on the surface of the liquid. After a few
seconds suddenly a fairly vigorous reaction starts. The aluminum foil dissolves
with the evolution of a colorless gas and formation of red/brown pieces of
copper. Lateron, the copper also dissolves again, with the formation of a
small amount of gas, which causes the air above the liquid to turn light brown.
Apparently the aluminum first dissolves, while producing hydrogen gas and
metallic copper. The metallic copper slowly dissolves, forming nitrogen oxide.