Sciencemadness Discussion Board - Pennies and vinegar

Pennies and vinegar

confusedpizza - 11-4-2014 at 10:12

Gen Chem student here. Likely a dumb question to follow.

When you put an old penny (pre-1982, so made of copper and zinc) in vinegar, which dissolves first - the copper or the zinc? Assuming the copper, does this reaction happen?

2Cu(s) + 2C2H3O2H(aq) + 2H2O(l) ⇆ Cu(C2H3O2)2(aq) + Cu(OH)2(aq) +4H+(aq)

I'm basing the reaction on the fact that vinegar is mostly acetic acid and water and Copper could combine with the hydroxide and the acetate ion. Does this reaction happen, and if not, what am I doing wrong?

DraconicAcid - 11-4-2014 at 10:17

The reaction as you've written it cannot happen, as it isn't balanced. You have no net charge on the reactants side, and four positive charges on the products.

For copper to react with any acid other than nitric, you need another oxidizing agent (in this case, oxygen from the air). Water will be produced.

confusedpizza - 11-4-2014 at 10:28

What happens if I boil it?

DraconicAcid - 11-4-2014 at 10:34

It will get hot. But it's still not going to allow an unbalanced equation to happen (are those electron supposed to just vanish?).

blogfast25 - 11-4-2014 at 10:39

Quote: Originally posted by DraconicAcid

It will get hot.

LOL.

C'mon, help him out of his misery.

[Edited on 11-4-2014 by blogfast25]

confusedpizza - 11-4-2014 at 10:44

Hahaha

So essentially I'm trying to figure out how something like this works:
http://www.ehow.com/how_8622662_make-glow-powder-household-i...

What is the reaction that is happening?

confusedpizza - 11-4-2014 at 10:46

Quote: Originally posted by blogfast25

Quote: Originally posted by DraconicAcid

It will get hot.

LOL.

C'mon, help him out of his misery.

[Edited on 11-4-2014 by blogfast25]

Thanks

(and it's *her* ;-P)

Zyklon-A - 11-4-2014 at 10:47

The copper and zinc isn't an alloy, it's ~98% zinc plated with ~2% copper, the copper will protect the zinc, so nothing will happen, in the reaction.

DraconicAcid - 11-4-2014 at 10:49

2 Cu + 4 HC₂H₃O₂ + O₂ --> 2 Cu(₂H₃O₂)₂ + 2 H₂O

gdflp - 11-4-2014 at 10:51

Try hydrogen peroxide, then the copper will dissolve.

@DraconicAcid Having fun? LOL

DraconicAcid - 11-4-2014 at 10:51

Quote: Originally posted by Zyklonb

The copper and zinc isn't an alloy, it's ~98% zinc plated with ~2% copper, the copper will protect the zinc, so nothing will happen, in the reaction.

That's after 1982; the OP specified pre-1982 pennies, which were 95% copper and 5% zinc.

gdflp - 11-4-2014 at 10:52

The pre-1982 pennies also had some tin in them I believe. At least, the really old ones did, they might have stopped that in 1944.

DraconicAcid - 11-4-2014 at 10:57

From Wiki: http://en.wikipedia.org/wiki/Penny_%28United_States_coin%29

1856–1864 88% copper, 12% nickel (also known as NS-12) 4.67
1864–1942 bronze (95% copper, 5% tin and zinc) 3.11
1943 zinc-coated steel (also known as 1943 steel cent) 2.67
1944–1946 brass (95% copper, 5% zinc) 3.11
1946–1962 bronze (95% copper, 5% tin and zinc)
1962–1981 brass (95% copper, 5% zinc)
1982 varies: brass (95% copper, 5% zinc) or copper-plated zinc (97.5% zinc, 2.5% copper)[7] 3.11 or 2.5
1983–present 97.5% zinc, 2.5% copper (core: 99.2% zinc, 0.8% copper; plating: pure copper)[8] 2.5

confusedpizza - 11-4-2014 at 11:04

Assuming 62-81 pennies. If I want to make glow in the dark powder, what do I do and why? I may actually even do it, but I really am primarily concerned with what's happening and why.

DraconicAcid - 11-4-2014 at 11:12

Isn't it the zinc sulphide that's phosphorescent?

HgDinis25 - 11-4-2014 at 11:12

When you add Copper to Acetic Acid you get nothing. However, Copper always has a thin oxide layer of Copper(II) Oxide. This will react with Acetic Acid:
CuO(s) + 2HAc(aq) --> Cu(Ac)2(aq) + H2O(l)
So, you've dropped the penny into Acetic Acid. The Copper(II) Oxide will react but Copper won't. However, in the course of time, Copper will be oxidized by Oxygen in the atmosphere, as follows:
2Cu(s) + O2(g) --> 2CuO(s)
And the Copper(II) Oxide produce will react further with Acetic Acid. And this is the entire process of dissolving Copper in Acetic Acid.
Now, when you boil the solution, you'll be speeding up the Oxidation reaction and feeding more Oxygen into the reaction mixture, so Copper will dissolve faster.

blogfast25 - 11-4-2014 at 13:11

Quote: Originally posted by HgDinis25

2Cu(s) + O2(g) --> 2CuO(s)
And the Copper(II) Oxide produce will react further with Acetic Acid. And this is the entire process of dissolving Copper in Acetic Acid.

No, it bloody well isn't. Even in vinegar the H3O+ concentration is high enough so that CuO cannot form, unless the acid has been depleted nearly completely.

In essence:

HOAc + H2O < === > H3O+ + OAc-

O2 + 4 H3O+ + 4 e === > 6 H2O (reduction of O2 to water in acid conditions)

Cu === > Cu2+ + 2 e (oxidation of copper to cupric ions)

Cu(s) + 1/2 O2(aq) + 2 H3O+ === > Cu2+(aq) + 3 H2O(l)

The acetate ions are spectators. No CuO is ever formed.

But this is a very slow process. Hydrogen peroxide would speed it up considerably.

[Edited on 11-4-2014 by blogfast25]

vmelkon - 14-4-2014 at 12:36

I think HgDinis means that copper gets covered by Cu(OH)2/CuCO3 mixture, called patina.

Anyway as for the original question, I would stick with pure chemicals, specially for making glow in the dark powder. Use electrical wire as your source of copper.

One method is to have some ZnSO4 dissolves in water. Bubble some H2S into it. Filter out the ZnS. Make a very dilute solution of CuSO4 (I think 0.005 M).
Add to the ZnS and heat strongly.

annaandherdad - 23-4-2014 at 16:37

confused, take a look at the youtube videos of Gizmodium for making ZnS and then glow-in-the-dark powders. If you want to start with pennies, try post 1982. A method we used to get pure ZnSO4 from these pennies is described at http://www.sciencemadness.org/talk/viewthread.php?tid=23059#...

HgDinis25 - 23-4-2014 at 17:13

Quote: Originally posted by blogfast25

Quote: Originally posted by HgDinis25

2Cu(s) + O2(g) --> 2CuO(s)
And the Copper(II) Oxide produce will react further with Acetic Acid. And this is the entire process of dissolving Copper in Acetic Acid.

http://www.newton.dep.anl.gov/askasci/chem03/chem03505.htm

Texium - 23-4-2014 at 18:33

I didn't want to start a new thread, so I figured I'd post this here since it's all about pennies.
A few weeks ago I dissolved the zinc core of a new penny in some HCl to obtain the thin copper jacket, and I figured I'd boil down the remaining solution to obtain zinc chloride for future use. I did this successfully.
The only issue was that it was a rather brownish tan color instead of white like zinc chloride is supposed to be. I started with a clean penny, so there shouldn't have been impurities from the exterior, and I didn't use an oxidizer, so all of the copper is intact.
Does anybody know what might have caused this impurity?

macckone - 24-4-2014 at 04:35

The core isn't pure zinc. I don't know what the alloy is but suspect
there are copper and aluminum in it. DraconicAcid posted that the core is .8%
copper with a reference.
And it is possible some small amount of copper was dissolved from the plating.
Finally if there are iron contaminants in your HCl, it will be a contaminant.
Recrystallizing your zinc chloride is probably your best bet for a pure product.
My suspicion is that the contaminant is iron given the color. copper would
be more greenish.

You would want to dissolve 2/3rds of your zinc chloride in minimum water,
let stand and filter. The impurities should not dissolve as none of them are
likely to be as soluble as the zinc chloride. Then add some pure HCl to the
zinc chloride and crystallize it. The HCl is necessary to prevent oxide formation.
HCl can be purified by distillation in glass equipment as the 20% azeotrope
to remove iron.

Texium - 24-4-2014 at 08:30

Thanks for the advice, my HCl is quite pure though. I've used it for many other purposes and there was no contamination from it. I think that it would be more likely that the impurities are from the coin itself. Maybe pennies contain a small amount of iron as well as copper and aluminum? I'll redo it with a few more pennies and see if I get the same result, and if I do then I'll recrystallize that larger amount of zinc chloride.

annaandherdad - 24-4-2014 at 17:16

For the content of current american pennies, see the link:

http://www.sciencemadness.org/talk/viewthread.php?tid=23059#...