Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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anhydrous chromic acid : CrO3
ammonium dichromate : (NH4)2Cr2O7
sodium chromate : Na2CrO4
cesium chloride : CsCl
Class:
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elem=Cr,Cs
precipitation
Summary:
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Cesium dichromate is very sparingly soluble in cold water, while cesium
chromate is much more soluble in cold water.
In warm water, the solubility of the dichromate is much higher.
Description:
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Dissolve some cesium chloride in water and set this solution aside.
Dissolve some ammonium dichromate (or sodium dichromate) in water and add the
solution of cesium chloride: A brighly colored yellow/orange precipitate is
formed, which is somewhat flocculent.
Use the same solutions as described above, but use a 3 to 4 times as low a
concentration of both solutions: When the solutions are mixed, then at first no
precipitate is formed, but after a few tens of seconds, fine particles settle
at the bottom. When this liquid is shaken, then soon all particles grow larger
and quite some precipitate is formed again.
Put the precipitates of the above two experiments and the liquid above that in
a small beaker and heat the contents of the beaker: Fiarly quickly, the
precipitate dissolves and a deep orange solution is obtained.
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Prepare a fairly concentrated solution of sodium chromate and add a solution of
cesium chloride: No precipitate is formed.
Add a few drops of a solution of CrO3: Immediately a dirty orange precipitate
is formed.
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Isolate some of the precipitate and then add some of this precipitate to water:
Only a small part of the precipitate dissolves, also after prolonged shaking
of the liquid. Cesium dichromate only is very sparingly soluble.
Add a small amount of solid sodium hydroxide: The sodium hydroxide and the
orange solid both quickly dissolve now. The resulting liquid has an intense
yellow color. The addition of the sodium hydroxide causes the dichromate to
be converted to chromate and now the cesium salt quickly dissolves. Cesium
chromate hence is much more soluble than cesium dichromate.