Description of experiment
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Needed compounds:
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sodium nitrite : NaNO2
dimethyl sulfoxide : (CH3)2SO
cupric chloride dihydrate : CuCl2 . 2H2O
Class:
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elem=C,N,Cu
organic
coordination
Summary:
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Copper (II) chloride and nitrite gives a deep green complex in water. This
combination gives a dark brown complex in DMSO.
Description:
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Sequence 1
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Add some solid sodium nitrite and solid copper (II) chloride dihydrate to each
other and then add a small amount of water: Both solids quickly dissolve and
the liquid becomes nicely deep green. The color is not really brilliant, it
definitely is green, but a somewhat more moss-like color.
Wait a few hours: A light green precipitate has settled at the bottom and some
light green solid is present at the surface of the liquid. The liquid itself
still is deep green.
Sequence 2
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Heat some cyan copper (II) chloride dihydrate, until all water is removed. A
dark brown solid of anhydrous copper (II) chloride is obtained.
Dissolve the brown anhydrous copper (II) chloride in some DMSO: A deep yellow
solution is obtained, with a very faint green/brown hue. The liquid remains
clear.
Add some solid sodium nitrite: The solid dissolves and the liquid becomes dark
brown. The liquid, sticking to the glass looks deep yellow with a brownish
tinge. The liquid really is dark after adding the sodium nitrite, it is much
darker than the aqueous solution, which has a similar copper and nitrite
concentration.
Wait for several hours: The liquid still is clear. The color has shifted
towards green. It still is brown, but more like a green/brown.
Remarks
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Copper forms a deep green complex with nitrite, which slowly decomposes in
water.
In DMSO, probably a mixed complex is formed, with DMSO, nitrite and possibly
chloride ligands.