Description of experiment
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Needed compounds:
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hydrogen peroxide : H2O2
sulphuric acid : H2SO4
potassium dichromate : K2Cr2O7
Class:
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elem=Cr
coordination
redox
Summary:
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When dichromate is brought in contact with peroxide, then after an initial
transient, a green variation of chromium (III) is produced. This compound,
however, slowly changes to a bluish/violet compound.
Description:
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Add an excess amount of hydrogen peroxide (3% by weight) to a solution of
K2Cr2O7 in dilute H2SO4 (1 mol/l): The liquid becomes intense blue and starts
foaming. After a few minutes, the liquid has become much lighter and its color
has changed to green (color of Cr3+ in many coordination complexes).
Let stand for one week: Color of liquid has shifted towards blue. When viewed
under SL light, it looks greenish blue, when viewed under tungsten light it
looks blue/violet.