Description of experiment
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Needed compounds:
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potassium dichromate : K2Cr2O7
hydrochloric acid : HCl
Class:
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elem=Cr
redox
Summary:
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Dichromate can be reduced by hydrochloric acid with some difficulty.
Description:
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Add some solid K2Cr2O7 to hydrochloric acid (appr. 20% by weight): The solid
dissolves and the liquid becomes dark orange/red. It becomes darker, than
when it is dissolved in the same volume of water. Apparently condensation
products are formed, due to the high acidity (e.g. [Cr3O10]2- or even higher
chromates).
Heat the liquid and boil for a while: The liquid becomes darker. After a few
minutes it is dark brown. On cooling down, it does not revert to its red/orange
color. The smell of chlorine can be observed, although it is not very strong.