Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
-----------------
potassium chromate : K2CrO4
potassium dichromate : K2Cr2O7
thallous nitrate : TlNO3
Class:
------
elem=Cr,Tl
precipitation
Summary:
--------
Thallium(I) chromate and thallium(I) dichromate both are insoluble (or at most
marginally soluble) in water. Thallium(I) is not a sufficiently strong reductor
to get the hexavalent chromium reduced.
Description:
------------
Dissolve some thallium(I) nitrate in water and keep this aside.
In one test tube, dissolve some potassium dichromate: A clear orange solution
is obtained.
In another test tube, dissolve some potassium chromate: A clear yellow solution
is obtained.
Add a small amount of the solution of thallium(I) nitrate to both the orange
and the yellow solution: In both cases a flocculent precipitate is formed,
which slowly settles to the bottom. With the dichromate, the precipitate is
golden yellow, close to orange, but not as bright orange as the crystals of
potassium dichromate. With the chromate, the precipitate is very bright yellow.
When the two precipitates are kept near each other, then the dichromate
precipitate looks orange, compared to the bright yellow
---------------------------------------------------
Both thallium(I) chromate and thallium(I) dichromate are insoluble, and both
have the characteristic color of the anion.