Description of experiment
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Needed compounds:
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sodium hydroxide : NaOH
hydrochloric acid : HCl
chrome alum : KCr(SO4)2 . 12H2O
EDTA tetra sodium : (NaOOC CH2)2 N CH2 CH2 N (CH2 COONa)2
Class:
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elem=Cr
precipitation
coordination
Summary:
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EDTA builds pink complexes with chromium (III). This complex is destroyed
in strongly alkaline environments.
Description:
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Add a solution of chrome alum to a solution of EDTA Na4: Formation of a
grey precipitate and the liquid above the precipitate turns pink/purple
(color resembles that of a very dilute solution of KMnO4).
Add an excess amount of HCl (10% by weight) to the pink liquid with
grey precipitate: The precipitate dissolves, the liquid becomes clear
and purple.
Add an excess amount of a solution of NaOH: Liquid becomes clear and green.