LanthanumK
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Reaction of copper(II) chloride with aluminium
What is the formula for this reaction? It could be any of these.
3 CuCl2 + 2 Al --> 2 AlCl3 + 3 Cu
3 CuCl2 + 4 Al + 6 H2O --> 2 Al(OH)3 + 3 H2 + 2 AlCl3 + 3 Cu
6 CuCl2 + 3 H2O + 4 Al --> 4 AlCl3 + 3 Cu2O + 3 H2
I believe that it is the latter because hydrogen bubbles are emitted and the resulting red precipitate dissolves in ammonia to make a colorless
solution which turns blue upon aerial oxidation. The solution resulting from the reaction is not turbid.
I have not seen the latter reaction mentioned anywhere on the Internet, though.
Any thoughts or reactions that I missed? I know that all of these reactions are technically incorrect because some of the chemicals are dissociated in
solution.
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hkparker
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<a target="tab" href="http://woelen.homescience.net/science/chem/exps/cu+al/index.html">From woelen's awesome website:</a>
| Quote: |
The following reactions occur:
2Al(s) + 6H2O(aq) → 2Al(OH)3(s) + 3H2(g)
2Al(s) + 3CuCl42-(aq) → 2AlCl4–(aq) + 4Cl–(aq) + 3Cu(s)
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The whole article is a must read.
[Edited on 1-6-2011 by hkparker]
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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IrC
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2 Al + 3 CuCl2 --> 2 AlCl3 + 3 Cu is valid.
Cannot find a reference for the last two but:
AlCl3 + 3H2O = Al(OH)3 + 3HCl,
2Al + 6HCl = 2AlCl3 + 3H2,
2Al + 6 H2O = 2Al(OH)3 + 3 H2,
2Al + 3H2O = Al2O3 + 6H,
2AlCl3 . 6H2O = Al2O3 + 6HCl + 9H2O
So I wonder if stripping the oxide layer off the Al does not lead to some of these reactions while some of the others are going on as side reactions?
hkparker must have posted while I was typing this, more info is good. Reading Woelens page makes me wonder if some of these side reactions are not
part of the answer to the questions he has on that page. Damn I love Woelen's work!
[Edited on 6-1-2011 by IrC]
"Science is the belief in the ignorance of the experts" Richard Feynman
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LanthanumK
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When I do the reaction with copper(II) chloride I don't get a turbid solution though. I read through the article and woelen gets a turbid solution,
which shows that Al(OH)3 is made.
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IrC
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You did say hydrogen is coming up, the reaction 2Al + 3H2O = Al2O3 + 6H is very likely going on with fresh surfaces on the Al after other reactions
have taken place. I think you are merely looking at a more complex series of events than you may at first think you have.
"Science is the belief in the ignorance of the experts" Richard Feynman
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sternman318
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On Woelen's page:
Probably the aluminium/copper reaction is also fast, due to formation of a copper-aluminium electrolytic couple, which causes the aluminium to be
oxidized quickly, while hydrogen from the water is produced at the copper side of the connected metal-pair.
What exactly is an electrolytic couple?
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IrC
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Two metals in contact, Al at bottom and Cu near top of the galvanic series. Like using two dis-similar metals in an electrolyte to create a battery,
the Al-Cu contact sets up a voltage potential where in this case the Cu causes the Al to be eaten up faster. I am positive this is what Woelen was
saying, i.e. the Al is more negative in terms of electrochemical potential. The potential difference attracts positive ions to one side and negative
to the other. IIRC in effect you can say oxidation at one end and reduction at the other. Say Al is one in the series and Cu is 10. All lower metals
will be accelerated in their corrosion by all metals higher up in the series. I may be explaining this poorly but read the PDF I am including, it may
aid your understanding. No idea why the file does not include Mg in the chart, it would help people to understand why a Mg sacrificial anode is used
in swamp coolers to prevent the cooler tank from rusting out. An unfortunate omission by the author considering the swamp cooler uses this idea more
than any other device common in the desert southwest.
http://en.wikipedia.org/wiki/Galvanic_anode
Attachment: Preventing Electrolysis.pdf (11kB)
This file has been downloaded 572 times
Edit to add: since Al is 1 in the PDF think of Mg as zero, or most negative of all metals on the chart (where 0 to 12 merely indicates position in
terms of relative electro-negativity, 0 being most negative and 12 most positive).
[Edited on 6-2-2011 by IrC]
"Science is the belief in the ignorance of the experts" Richard Feynman
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Mr. Wizard
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Quote: Originally posted by sternman318  | On Woelen's page:
Probably the aluminium/copper reaction is also fast, due to formation of a copper-aluminium electrolytic couple, which causes the aluminium to be
oxidized quickly, while hydrogen from the water is produced at the copper side of the connected metal-pair.
What exactly is an electrolytic couple? |
Think of it as a short circuited battery. The active material gets used up more quickly, as the two metals (usually) are in contact, allowing current
to flow.
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