G.Lowell
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Molar calculations - lame question
I am making CuCl2 - Cu (s) + 2 HCl (aq) -> CuCl2 + H2
My calculation is this:
Molar weight of copper is ~63 g/mol thus I have 10/63= ~ 0.16 mol of copper.
Making CuCl2 from it should take 2*0.16 ~ 0.32 mol of acid.
32% solution HCl ~ 10 mol which means 1mol ~ 100ml so I need 0.32*100ml ~ 32 ml of HCl.
But after a week only 3 grams of copper are dissolved
Sorry for so simple question, but what could be wrong with my calculation ?
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aga
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I'd be surprised if that even worked at all.
Perhaps 3g of something else has been consumed by the acid ?
Edit :
As per the wiki :
http://en.wikipedia.org/wiki/Copper%28II%29_chloride
"Copper(II) chloride is prepared commercially by the action of chlorination of copper:
Cu + Cl2 + 2 H2O → CuCl2(H2O)2
Copper metal itself cannot be oxidised by hydrochloric acid, but copper-containing bases such as the hydroxide, oxide, or copper(II) carbonate can be
reacted with hydrochloric acid."
[Edited on 3-4-2015 by aga]
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G.Lowell
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The piece of copper was 10 gram. Now is 7. Solution is brown.
+air was bubbling through the solution.
[Edited on 3-4-2015 by G.Lowell]
[Edited on 3-4-2015 by G.Lowell]
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aga
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It still can't defy the laws of physics.
Most likely is that the copper isn't pure or 'clean' and the HCl has dissolved 3g of crud that was in your Cu to start with.
Your reasoning on the Molar calculations is perfectly sound, just that Cu does not react with HCl is all.
As far as i know, the only common acid that will react with Cu is HNO3.
Edit:
Here's a nice prep for CuCl2 :
http://amateurchemistry.weebly.com/synthesis-of-copper-ii-ch...
[Edited on 3-4-2015 by aga]
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gdflp
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Yes aga, hydrochloric acid can dissolve copper for the following reason. Air from the bubbler oxidizes the surface of the copper by
the following process 2Cu + O2 --> 2CuO, the hydrochloric acid then attacks the copper oxide by CuO + 2HCl --> CuCl2 +
H2O. This leaves a fresh surface of copper which can then be oxidized and the process repeats. G.Lowell your math looks
correct, the only thing that I would recommend is diluting the acid to ~10% with water to increase the solubility of the copper chloride and thus
increase the rate of the reaction. Because the oxidation of copper is a slow process, this reaction does take a long time.
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blogfast25
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Firstly, the brown colour described by G.Lowell is almost certainly due to a mixed oxidation state Cu(I)/Cu(II) complex that's been described on this
forum several times (I'll see if I can dig it up). I've seen it myself and it is well described in the peer reviewed literature. Copper(II) hexaqua
ions are blue, Cu(I) is generally colourless.
Copper will dissolve slowly in HCl, but only IF there's an oxidising agent like hydrogen peroxide or air oxygen present. Copper is not an
electropositive element and cannot be oxidised by H<sub>3</sub>O<sup>+</sup> cations (the only oxidising species present in
dilute solutions of HCl and other acids with 'non-oxidising' conjugated bases).
CuO doesn't form in this process, not in acidic conditions, instead the likely oxidation reaction in acid conditions is:
Cu(s) + 1/2 O<sub>2</sub>(g) + 2 H<sup>+</sup>(aq) ===> Cu<sup>2+</sup>(aq) + H<sub>2</sub>O(l)
Copper metal reacts with Cu<sup>2+</sup> to form Cu(I), the source of the Cu(I)/Cu(II) complex most likely. Removing the excess copper and
allowing the Cu(I) to be oxidised to Cu(II) should remove the brown complex.
There's little reason to believe diluter HCl would work faster here.
In the link in aga's post, copper carbonate is represented by CuCO3. That's incorrect: it's copper basic carbonate,
Cu<sub>2</sub>CO<sub>3</sub>(OH)<sub>2</sub>.
A few experiments by woelen on the copper(I,II) mixed oxidation complex:
http://woelen.homescience.net/science/chem/riddles/copperI+c...
http://woelen.homescience.net/science/chem/riddles/copperI+c...
http://woelen.homescience.net/science/chem/riddles/copperI+c...
[Edited on 3-4-2015 by blogfast25]
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aga
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So No, HCl doesn't dissolve Cu.
Glad that's cleared up !
Sorry to have missed the significant Cu + O2 reaction going on.
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blogfast25
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HCl and other acids with non-oxidising conjugated bases will not dissolve any non-electropositive elements.
Simply put, the general reaction:
M(s) + z H<sup>+</sup> === > M<sup>z+</sup> + z/2 H<sub>2</sub>
…cannot proceed if the Reduction Potential of the metal M is positive (> 0 V) (somewhat paradoxically perhaps these metals are NOT
electropositive).
But ‘external’ oxidisers can dissolve these metals in acids anyway (generally more slowly). See e.g. the dissolution of lead in acetic acid and
hydrogen peroxide.
[Edited on 3-4-2015 by blogfast25]
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Loptr
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Quote: Originally posted by aga  | So No, HCl doesn't dissolve Cu.
Glad that's cleared up !
Sorry to have missed the significant Cu + O2 reaction going on. |
A lot of times the system being observed isn't exactly as we understand it to be. So if we observe behavior that doesn't line up with a given law or
accepted mechanism, there is more than likely more to our particular reaction than we are initially aware of. I hate when I see claims regarding how
something is breaking a law of physics or what have you, as most of the time, it turns out there is indeed something proceeding, just under different
circumstances and not according to our understanding. We tend to be the break in the chain majority of the time. 
Are your reagents pure? Have you excluded moisture? Are your additions allowing for temperatures higher or localized concentrations than anticipated?
Are there stabilizing agents added to your chemicals. (phosphoric acid for h2o2, etc., etc.)
[Edited on 3-4-2015 by Loptr]
[Edited on 3-4-2015 by Loptr]
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brubei
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just look at the electropotentiel of your redox equations https://en.wikipedia.org/wiki/Standard_electrode_potential_(data_page)
Cu2+ + 2e- => Cu +0.33V
2 H+ + 2 e- => H2(g) +0.00V
The gamma rule says you need oxydant with greater potential than the Cué+/Cu couple. Of course the couple H+/H2 is not one of them.
Non minéral or halogenic couple with higher potentiel requires oxygenated water:
H2O2(aq) + 2 H+ + 2 e− => 2 H2O +1.78V
Atmospheric O2 dissolved in your water explain the slow dissolution of copper despite the thermodynamics rules.
[Edited on 3-4-2015 by brubei]
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G.Lowell
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When extra water was added into solution reaction started again, copper has only 4 grams now. To speed reaction up I added H2O2. Solution changed
color to green which is exactly what I need.  Thanks to all!
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Deathunter88
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| Quote: Originally posted by aga | It still can't defy the laws of physics.
Most likely is that the copper isn't pure or 'clean' and the HCl has dissolved 3g of crud that was in your Cu to start with.
Your reasoning on the Molar calculations is perfectly sound, just that Cu does not react with HCl is all.
As far as i know, the only common acid that will react with Cu is HNO3.
Edit:
Here's a nice prep for CuCl2 :
http://amateurchemistry.weebly.com/synthesis-of-copper-ii-ch...
[Edited on 3-4-2015 by aga] |
In the URL you linked the author used Copper (II) Carbonate with the formula CuCO3, but most copper carbonate that is available is basic copper
carbonate. Will using basic copper carbonate give the same result?
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blogfast25
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| Quote: Originally posted by Deathunter88 | | In the URL you linked the author used Copper (II) Carbonate with the formula CuCO3, but most copper carbonate that is available is basic copper
carbonate. Will using basic copper carbonate give the same result? |
It's not 'most', it's ALL: CuCO3 simply does not exist.
Copper basic carbonate will also dissolve in HCl:
Cu2CO3(OH)2(s) + 4 HCl(aq) === > 2 CuCl2(aq) + 3 H2O(l) + CO2(g)
[Edited on 5-4-2015 by blogfast25]
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gdflp
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At STP. At high temperatures and pressures in a CO2 atmosphere, CuCO3 has been synthesized, it just only exists under these
extreme conditions. Here is a link to the abstract of one article http://onlinelibrary.wiley.com/doi/10.1002/zaac.19744100207/...
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aga
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What does 20kb mean in terms of pressure ?
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DraconicAcid
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Copper will slowly react with hydrochloric acid in the presence of air, as blogfast says. This reaction is autocatalytic- the more copper ions there
are in solution, the faster it goes.
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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blogfast25
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I assume it means 20 kilobar, which is about 20 atm. But there's no SI unit symbol 'kb'. Bad Science by the author.
[Edited on 5-4-2015 by blogfast25]
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