Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrochloric acid : HCl
hydrogen peroxide : H2O2
bleach : NaClO
sodium hydroxide : NaOH
chrome alum : KCr(SO4)2 . 12H2O
Class:
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elem=Cr,Cl
redox
Summary:
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Bleach is capable of oxidizing chromium (III) to its hexavalent state, but
this is not accomplished easily and completely.
Description:
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Add an excess amount of a solution of NaOH to a solution of chrome alum: The
resulting liquid becomes clear and green.
Add a large amount of bleach: The liquid remains green.
Add to appr. 60 C for several minutes: The liquid slowly turns yellow/green.
After a few minutes of heating and shaking, the final color is yellow with
a slight green shade, it looks as a not completely ripe lemon.
Add a mixture of HCl (10% by weight) and H2O2 (3% by weight): The liquid
starts foaming vigorously and it turns indigo/blue. After a few seconds
the intense indigo/blue color has faded again and the liquid is pale
yellow/green again.
Remark: This sequence of experiments shows that bleach (hypochlorite) is
capable of oxidizing chromium (III) in alkaline environments to hexavalent
chromium, but this reaction does not occur quickly and needs some heating.