Description of experiment
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Needed compounds:
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formaldehyde : CH2O
hydrogen peroxide : H2O2
sodium sulfite : Na2SO3
oxalic acid : HOOC COOH . 2H2O
ascorbic acid : C6H8O6
nitric acid : HNO3
sodium dichromate dihydrate : Na2Cr2O7.2H2O
ammonium chloride : NH4Cl
Class:
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elem=Cr
coordination
redox
Summary:
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Chromium (III) gives coordination complexes of all kinds of colours, when
formed from a redox reaction, starting with dichromate.
Description:
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Create a solution of ammonium chloride and sodium dichromate in dilute HNO3
(appr 1 mol/l) and add diverse reductor and observe the colour of the
resulting liquidi, containing the resulting chromium (III) species:
ascorbic acid: fast reaction, resulting in greygreen/greyblue liquid
oxalic acid: reaction requires heating, resulting in slow formation of
a liquid which looks grey, when viewed with TL-light, grey/violet
when viewed with SL-light and purple when viewed with tungsten
light.
sodium sulfite: fast reaction, rsulting in a green liquid. The green is
a nice bright green, with a bluish hue.
hydrogen peroxide: After an initial dark blue/indigo transient the liquid
slowly turns green, while developing a gas (oxygen). The green
colour is not a bright colour as with sulfite, it is more greyish
green, especially when viewed with tungsten light.
formaldehyde (solution appr. 35 % by weight): A solw reaction occurs. The
resulting liquid is green when viewed with TL-light and it looks
green/grey when viewed with tungsten light.