toothpick93
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Strange colour change Happening
So i was etching large bits of copper pipe which was pretty bardly corroded. I then had some small bits of copper so i thought to do a close up view
and when i mixed the h2o + h2o2 solution with the hcl, well it made the solution turn brown. As the copper reacted with the solution, it changed to
the green colour of copper chloride. so why the brown colour?
No pictures, only part of the video, just watch the first 5 seconds to see what i mean. Or spend 2 minutes watching the copper corrosion disolve 
http://www.youtube.com/watch?v=HVWrlu68OO4&feature=youtu.be
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Fantasma4500
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ive experienced the same thing, but didnt think further about it..
when i did it i wanted to etch some osmium (i believe it was?) from a long lightbulb
when adding the H2O2 it somehow bubbles alot and smells like chlorine (H2O2 + HCl > Cl2?) it should make some stronger etching solution, didnt work
for me with HCl on copper and H2O2 added in, but there was the same bubbling tho no actual reaction with the copper as i remember..
but also with steel + unknown metal this effect / reaction occurs so i doubt its anything specific with the copper, tho it could of produced CuO to
then react with the HCl again..
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Mixell
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the CuCl2(-) anion (Copper I chloride dissolved in concentrated HCl) is brown, but you say that the brown color was formed without the copper? just
HCl and H2O2? Is there a chance one of your reagents my be impure?
H2O2 can oxidize Cl-, but the solution should be just slightly greenish-yellow (barely noticeable), not brown...
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DraconicAcid
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Quote: Originally posted by Mixell  | the CuCl2(-) anion (Copper I chloride dissolved in concentrated HCl) is brown, but you say that the brown color was formed without the copper? just
HCl and H2O2? Is there a chance one of your reagents my be impure?
H2O2 can oxidize Cl-, but the solution should be just slightly greenish-yellow (barely noticeable), not brown... |
I thought that it was CuCl4(2-) that was brown (Cu(I) is a d10 system, and isn't expected to be colourful). When you dissolve CuCl in HCl, you always
get some of the Cu(II) ion forming, since there is some oxygen dissolved in the acid (unless you've degassed it), and the solution is exposed to air.
If you got brown when you first added the copper, and then that faded to green as the ratio of chloride to copper ions decreased, that would make
sense...
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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woelen
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| Quote: Originally posted by Mixell | the CuCl2(-) anion (Copper I chloride dissolved in concentrated HCl) is brown, but you say that the brown color was formed without the copper? just
HCl and H2O2? Is there a chance one of your reagents my be impure?
H2O2 can oxidize Cl-, but the solution should be just slightly greenish-yellow (barely noticeable), not brown... |
Copper forms a mixed copper(I)/copper(II) complex in strong HCl.
CuCl2(-) is colorless, CuCl4(2-) is green/yellow, but when both are present (and that easily is the case in aqueous copper(I) solutions, which are
exposed to air) then a very dark brown complex is formed.
Have a look at this: http://woelen.homescience.net/science/chem/riddles/copperI+c...
And especially the first part of the fifth experiment from that page may be interesting for you. In that experiment a colorless solution of copper(I)
is oxidized by oxygen from air and a dark brown compound is formed.
http://woelen.homescience.net/science/chem/riddles/copperI+c...
[Edited on 4-3-13 by woelen]
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Mixell
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Yes, now that I think about it, the mixed-oxidation state compound sounds more logical.
But it doesn't explain the color if there was no copper present in the vessel or in the solution prior to the submergence of the pipe.
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