Volanschemia
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Aqueous Copper(II) Nitrate and Magnesium Ribbon
Hi everyone.
I just did the famous silver tree reaction (adding copper metal to a solution of silver(I) nitrate which forms silver metal and copper(II) nitrate).
I filtered off the copper(II) nitrate solution and kept the silver crystals and just as I was about to discard the solution I thought, what if I put a
more reactive metal than copper in? Would it make a copper tree? I had some magnesium ribbon laying around so chucked a few bits in.
Over the course of about 5 mins the solution started to turn GREEN (not clear as I had expected) and bubbles started to evolve. Also the magnesium
ribbon began to get coated with a black substance which I am guessing is the copper precipitate, although it is more black than red (possibly been
oxidized by magnesium nitrate to copper(II) oxide???).
Just wondering why the solution has turned green and why it is forming bubbles.
It is still reacting at the moment so it might turn clear eventually. I will post back here with an update and some pictures soon.
Thanks!
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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DraconicAcid
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A solution of copper ions is acidic, so you will get the reaction:
Cu2+ + Mg + 2 H2O -> Mg2+ + H2 + Cu(OH)2
The black is probably finely divided copper, though.
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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Volanschemia
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Quote: Originally posted by DraconicAcid  | A solution of copper ions is acidic, so you will get the reaction:
Cu2+ + Mg + 2 H2O -> Mg2+ + H2 + Cu(OH)2
The black is probably finely divided copper, though. |
Thanks for your answer.
So there is two reactions happening?
The one above and Mg + Cu(NO3)2 = Mg(NO3)2 + Cu
So what is causing the green colour? As far as I know Mn2+ is pink.
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
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diddi
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green is most likely due to a complex involving Cu2+
Cu metal is black when precipitated, so it is not CuO
Because Mg is quite reactive (E° =-2.38) , it is capable of displacing H+ from H2O
so there are 2 competing reactions, and the bulk of the Mg will be consumed by the H2O I would expect
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Volanschemia
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Thanks for your reply diddi.
I completely forgot about Mg's reactivity with water.
What would the Cu2+ be complexing with?
It seems there is actually three reactions happening, because there is a blue precipitate forming on the bottom of the beaker.
I'm guessing it is the reaction DraconicAcid mentioned.
There's a lot going on!
I will wait for the reaction to cease then see what the products are.
[Edited on 24-1-2015 by TheAustralianScientist]
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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DraconicAcid
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But there is no manganese in solution- magnesium is colourless. The green colour would be some copper compound.
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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Volanschemia
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Sorry about that! 
I'm sure it's not the first time someone confused Manganese and Magnesium.
Any idea what copper compound might be. As far as I know the only ions the copper could react with are NO3- or OH-, both of which form
blue compounds with copper.
The only green copper compound I know of is CuCl2 and there was no Cl- in there.
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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diddi
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the attachment of various ligands will effect the colour you normally expect, by altering the energy levels in the d-orbital split. possible ligands
here are OH-, H2O, NO3-
Cu2+ is typically 4-coordinate and most structures are approximately square planer. so there could be some strange complex happening. cant say for
sure.
and dont forget there are still Ag+ ions in there
[Edited on 24-1-2015 by diddi]
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Dan Vizine
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Just curious, what other metals may be in your reagents? Was the copper chemically pure or from a source like wires or pipes?
Many chemists have famously been misled by assumptions based on the colors they observed which were actually from unexpected or undetected minor
impurities.
The black is the copper, no doubt. The bubbles are hydrogen, your faith in the electromotive series is reinforced. But, I suspect a metallic impurity.
Did you use tap water?
No denying diddi's point. Even though Jahn-Teller distortion is often though of as being about Oh molecules, it is important to copper, also. Those
energy level shifts can be pretty fluid.
So, it's hard to say for sure if it's one thing or the other or both.
[Edited on 26-1-2015 by Dan Vizine]
"All Your Children Are Poor Unfortunate Victims of Lies You Believe, a Plague Upon Your Ignorance that Keeps the Youth from the Truth They
Deserve"...F. Zappa
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Volanschemia
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I did use copper wire from electrical cables so there could be some metal impurites. There could also have been some CuO in there from oxidation of
the copper wire by AgNO3.
There is a light blue precipitate on the bottom of the beaker which I'm guessing is Copper(II) Hydroxide (will test later by heating to 60 degrees C),
so DraconicAcid's reaction happened as well.
| Quote: Originally posted by Dan Vizine | Just curious, what other metals may be in your reagents? Was the copper chemically pure or from a source like wires or pipes?
Many chemists have famously been misled by assumptions based on the colors they observed which were actually from unexpected or undetected minor
impurities.
The black is the copper, no doubt. The bubbles are hydrogen, your faith in the electromotive series is reinforced. But, I suspect a metallic impurity.
Did you use tap water?
No denying diddi's point. Even though Jahn-Teller distortion is often though of as being about Oh molecules, it is important to copper, also. Those
energy level shifts can be pretty fluid.
So, it's hard to say for sure if it's one thing or the other or both.
[Edited on 26-1-2015 by Dan Vizine] |
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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Volanschemia
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Here are some pictures.
The first two show the green colour during the reaction.
The second two show the reaction is finished and the solution is now colourless and there is a blue precipitate on the bottom of the beaker as well as
some copper powder. (Am I right in thinking that the disappearance of the green suggests a complex?)
The last one shows the products on a filter paper. I will test the blue precipitate when it dries to make sure it is Copper(II) Hydroxide, but I
don't know of any other insoluble blue Copper(II) compounds.
     
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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diddi
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looking here:
http://www.docbrown.info/page07/transition09Cu.htm
I see that a Cu(Cl-)4 complex is yellow/brown. in blue copper sln, this would appear green
so if there is any salt contamination from tap water etc, that could explain the colour.
you have mixed products in four filter paper, btw. will need recrystallization possible in acidic environment to separate them?
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Volanschemia
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I used distilled water in the reaction so I don't see how any Cl- ions could have gotten in there. Products on the filter paper would include:
Copper(II) Hydroxide
Copper(II) Nitrate (trace)
Silver(II) Nitrate (trace)
Magnesium(II) Nitrate
Magnesium Metal
Copper Metal
What do you mean by an acidic recrystallization?
| Quote: Originally posted by diddi | looking here:
http://www.docbrown.info/page07/transition09Cu.htm
I see that a Cu(Cl-)4 complex is yellow/brown. in blue copper sln, this would appear green
so if there is any salt contamination from tap water etc, that could explain the colour.
you have mixed products in four filter paper, btw. will need recrystallization possible in acidic environment to separate them?
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"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
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diddi
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recrystallization from acids is often a useful way of altering the solubility of compounds, so it may be that you can solvate one solid and leave
others behind.
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Volanschemia
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| Quote: Originally posted by diddi | recrystallization from acids is often a useful way of altering the solubility of compounds, so it may be that you can solvate one solid and leave
others behind.
|
So how would I go about doing that?
Would the Copper(II) Hydroxide dissolve in acid?
What acid would I use?
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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diddi
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readily: OH- + H+ = H2O
not sure about getting it back again without complexes tho. have to think about that. try looking up solubilities
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Volanschemia
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The problem with acid recrystallization is than if I add everything to an acid, any remaining NO3- ions will react to form Nitric Acid
which will dissolve the copper! So everything will dissolve which isn't the outcome we're after.
2HCl(aq) + Mg(NO3)2(aq) = MgCl2(aq) + 2HNO3(aq)
HCl + Cu(OH)2 = CuCl2 + H2O
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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