Draeger
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Brown crystals within green copper(II) chloride crystals - What are they?
So, I prepared some copper(II) chloride in this pathway:
- CuSO4 + NaHCO3 + H2O = CO2 + Na2SO4 + Cu(OH)2CO3
- (filtration to hopefully wash away the sodium)
- Cu(OH)2CO3 + HCl = CO2 + CuCl2
What could produce the brown color? I know that the anhydrous form is brown, but is it possible to create the anhydrous form by excessive heating?
Collected elements:
Al, Cu, Ga, C (coal), S, Zn, Na
Collected compounds:
Inorganic:
NaOH; NaHCO3; MnCl2; MnCO3; CuSO4; FeSO4; aq. 30-33% HCl; aq. NaClO; aq. 9,5% ammonia; aq. 94-96% H2SO4; aq. 3% H2O2
Organic:
citric acid, sodium acetate, sodium citrate, petroleum, mineral oil
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Bedlasky
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Dihydrate lose both waters at 100°C.
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Draeger
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Oh, then that explains it. My hotplate was likely far over 100°C. Thank you.
Collected elements:
Al, Cu, Ga, C (coal), S, Zn, Na
Collected compounds:
Inorganic:
NaOH; NaHCO3; MnCl2; MnCO3; CuSO4; FeSO4; aq. 30-33% HCl; aq. NaClO; aq. 9,5% ammonia; aq. 94-96% H2SO4; aq. 3% H2O2
Organic:
citric acid, sodium acetate, sodium citrate, petroleum, mineral oil
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woelen
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Copper(II) chloride indeed can be dehydrated by heating, but the resulting material becomes slightly impure. CuCl2.2H2O, when heated, shows two
reactions:
CuCl2.2H2O --> CuCl2 + 2 H2O
CuCl2.2H2O --> CuCl(OH) + HCl + H2O
The latter reaction only is a minor side reaction, but it is noticeable. The stronger the heating, the more this reaction occurs. So, if you want a
pure anhydrous product, then you have to heat very carefully. Very pure anhydrous CuCl2 can be made by heating the dihydrate in an atmosphere of dry
HCl. This is not easy to do in an amateur setting though. For any practical purpose, just heating it carefully is OK.
[Edited on 15-7-20 by woelen]
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Boffis
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In the presence of alkali and some alkaline earth metal salts copper II chloride forms chlorocuprate. With caesium chloride these crystallise easily
from aqueous solution and there are at least two of them, one brown and the other yellow. I suspect that you can also produce a similar compound from
sodium though it probably much more soluble and therefore harder to crystallise but will forms if the solution is dried hot. So it probably indicates
that you hadn't washed out all of the Na from your original ppt of copper carbonate.
Do your brown crystals dissolve again in water?
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woelen
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I have written a web page about these chlorocuprates and I made the cesium salt and isolated this. This, however, does not work with potassium and I
expect it to be even more difficult with sodium. In solution with excess chloride you indeed get the brown/yellow chlorocuprate, but crystallizing it
is not easily done with other than the cesium salt.
https://woelen.homescience.net/science/chem/exps/CsCuCl3/ind...
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Bedlasky
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Sodium salt can't be crystallized from solution. I tried it once and it didn't work.
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