Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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perchloric acid : HClO4
nitric acid : HNO3
hydrochloric acid : HCl
chromium : Cr
Class:
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elem=Cr
coordination
redox
Summary:
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Chromium metal does not dissolve al all in concentrated nitric acid, not even
when the acid is heated. It does dissolve in concentrated hydrochloric acid and
also in moderately concentrated perchloric acid, but in the latter some heating
is required.
Description:
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Add a spatula full of coarsely powdered high purity chromium metal to
concentrated nitric acid (appr. 65% HNO3): No reaction occurs. Even when the
acid is boiled, no reaction occurs.
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Add a spatula full of coarsely powdered high purity chromium metal to
concentrated hydrochloric acid (appr. 30% HCl): Immediately after adding the
acid to the metal, a slow reaction starts in which hydrogen is produced. After
a few seconds, the reaction becomes faster and there is a nice fairly vigorous
evolution of gas. The gas can be lighted and burns with a pop or a whoosh. It
is hydrogen gas. The reaction never becomes violent and the liquid does not
become hot. After a while, the liquid is clear and d
The liquid was set aside to cool down, with still some metal at the bottom.
Production of gas continued very slowly. After one day, all metal was gone and
a clear dark green solution is obtained.
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Add a spatula full of coarsely powdered high purity chromium metal to
moderately concentrated perchloric acid (appr. 20% HClO4): Initially no
reaction occurs. After a minute or so, tiny bubbles of gas can be observed, but
the reaction is very slow. Careful heating of the liquid makes the reaction go
faster, and once it is going, it keeps going fairly vigorously, but it never
becomes violent. Before all metal has dissolves, the reaction slows down again.
A blue/green solution is obtained, with a color, whic
Let the solution cool down and let it stand for a few days: All metal has
dissolved after these few days, but the color did not change. Still there is a
bluish shade with a green tinge.