LHcheM
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Question about copper (II) bromide/copper(II) bromide complex
I have been trying to prepare copper (II) bromide for quite a while. Without the access of HBr, I tried to prepare it by adding potassium bromide to
copper (II) nitrate.
However, the observation is strange, as soon as I added potassium bromide solution to a saturated solution of copper (II) nitrate, the color of the
solution changes from blue to green (exactly as that as conc HCl is added to Cu2+), then I leave it in an agar plate to evaporate, but the color of
the solution changes again, from green to yellow, then into a deep reddish-brown solution, so is this a further complex of Cu2+ with bromide? what is
the precise formula for this solution?
anyway, the volume of the solution no longer reduce when it reaches this dark brown color, and I put the agar plate into the refrigerator, dark brown
crystals deposited, but they are not grey black ones as described for CuBr2. So is this a salt of K xCuBr y? If yes, what's the formula? Or is it a
mixed species?
The crystals aren't hygroscopic as I scrapped it out from the agar plate.
For the deep brown solution, the addition of water will change its color from reddish brown, to dirty yellow/green, to green, then finally to blue
again. This confirmed the formation of complex with Cu2+, but I can't find the formula or description in books/internet, so can anyone help me to
solve this riddle?
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hkparker
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Perhaps this could help you:
http://woelen.homescience.net/science/chem/exps/copper_halog...
My YouTube Channel
"Nothing is too wonderful to be true if it be consistent with the laws of nature." -Michael Faraday
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Steve_hi
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You can Buy some HBr
http://www.elementalscientific.net/store/scripts/prodList.as...
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LHcheM
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Thanks for the reply, so I now understand that the aqueous species is [CuBr4]2-, so the dark crystals formed should be K2[CuBr4]? I have heard that
this complex is very hard to crystallize and that's why I doubt my prediction...
Well I actually live in Hong Kong where chemicals are rare enough, and suppliers are troublesome...Also the mail and checking procedures of dangerous
goods were tedious... That's why I synthesize most reagent myself..@@ Thanks anyway
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sternman318
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http://www.sciencemadness.org/talk/viewthread.php?tid=16598#...
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LHcheM
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I have watched that thread already, but it still can't explain whether the very dark brown crystals are Potassium Tetrabromocuprate (II) or Cupric
Bromide, but thanks anyway =)
I have searched for infos in "Inorganic Chemistry" by Catherine Housecroft, but there is not a single word describing the complex, and its properties,
so do anyone have any recommendable reference books that can confirm the formula?
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Jor
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Quote: Originally posted by LHcheM  | Thanks for the reply, so I now understand that the aqueous species is [CuBr4]2-, so the dark crystals formed should be K2[CuBr4]? I have heard that
this complex is very hard to crystallize and that's why I doubt my prediction...
Well I actually live in Hong Kong where chemicals are rare enough, and suppliers are troublesome...Also the mail and checking procedures of dangerous
goods were tedious... That's why I synthesize most reagent myself..@@ Thanks anyway |
I think the crystals are crystallised KBr containing some residuel solution on them or some co-crystallised bromocuprate complex wich gives them a
dark color.
If you have a distilling apparatus, KBr and sulfuric acid, aqeous HBr around 40% HBr) is very easy to make. Check:
http://www.sciencemadness.org/talk/viewthread.php?tid=10754
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