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Author: Subject: Copper hydroxide color
thesmug
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[*] posted on 18-4-2014 at 09:35
Copper hydroxide color


Just a few minutes ago I made some copper hydroxide, but it's a very dark green color, I've looked everywhere and I can't figure out what I did wrong or what my product actually is (I am almost 100% sure it's copper hydroxide, though). Has this happened to anyone else? I don't know what it is but whenever I try to make copper compounds they always come out the wrong color :mad:!
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jamit
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[*] posted on 18-4-2014 at 09:43


What was your starting material? And how concentrated was it?
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thesmug
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[*] posted on 18-4-2014 at 09:55


Starting materials were fully saturated copper sulfate solution and dry sodium hydroxide
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jamit
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[*] posted on 18-4-2014 at 10:39


You probably have a mixture of copper oxide and copper hydroxide. This mixture explains the green color. NaoH added to sat. Cuso4 will be an exothermic reaction producing lots of heat and that will convert the copper hydroxide formed into copper oxide... But it probably didn't convert all the copper hydroxide to copper oxide. Copper hydroxide is blue and copper oxide is black and when you mix these two colors you will get green. Your only option now is to heat the solution and it will convert all copper hydroxide to black copper oxide. Hope this help!
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WGTR
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[*] posted on 18-4-2014 at 10:48


If there's some carbonate in there, that could also add a greenish color. But yes, overheating copper hydroxide will
permanently dehydrate it, even in solution. It's better to form two separate solutions, one of CuSO4 and another of diluted
NaOH, let the NaOH solution cool down, and then mix them together. Dropping dry NaOH pellets into CuSO4 solution will
most likely cause localized heating and dehydration of the Cu(OH)2.
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thesmug
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[*] posted on 18-4-2014 at 11:10


WGTR that's what I did. Both solutions were very cold and formed the green precipitate instantly.


[Edited on 4/18/14 by thesmug]
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WGTR
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[*] posted on 18-4-2014 at 11:26


If it wasn't overheated, then, perhaps there is carbonate contamination in the NaOH. That's fairly common. Perhaps
test a small amount of the precipitate with an acid to check for CO2. When I've made Cu(OH)2 I've used the same
chemicals that you did, but it has always been a bluish color, unless I warmed it over 50°C or so. Cu(OH)2 that I've
slightly overheated turned dark green when wet. If I had left it longer it would have turned completely black.
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