querjek
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Setup for Preparation of Zinc Chloride from a Penny + HCl?
Hello,
I've read that zinc chloride may be produced by gassing zinc metal with HCl, or by simply dropping zinc into HCl acid.
I've also heard that American pennies made after 1982 are roughly 95% zinc with a thin copper coating on the outside.
How might one go about removing the copper from a penny, and past that, would the remaining zinc be malleable to crush finely?
Although dropping a penny into HCl solution would work easily, it seems that recovering anhydrous ZnCl2 may be troublesome.
Any input would be greatly appreciated--thanks!
it's all about chemistry.
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not_important
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It's closer to 98% zinc. Selectively dissolving the copper can be done, but it's a bother. You can abrade or sandblast if off, losing some zinc in
the process. Or you can just dissolve the zinc away from the copper:
Nick the penny to expose the zinc base, treat with moderately strong HCl, calculating how much of that acid is needed to dissolve roughly 95% of the
zinc. The copper surface and slight excess of zinc will remain as a shell, just filter that out, rinse well several times, and leave about
where someone will attempt to pick the filmy shell up.
It is somewhat bothersome to get anhydrous ZnCl2. Evaporating the solution until mushy, filtering off the remaining mother liquor, and drying in a
vacuum will give the hydrate. After that you're stuck with methods such as passing gaseous HCl over the hydrated ZnCl2 while heating, repeatedly
adding some concentrated HCl (~35%) and heating to dryness, mixing with NH4Cl and heating to drive off water and then the NH4Cl4, or some other
method.
Remember that technical grade hydrochloric acid likely contains iron. When dissolving the pennies any iron in the acid will plate out on the zinc, one
reason to use less acid than needed to dissolve all the zinc.
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Ozone
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The easiest way I found was to grasp the penny in a pair of tongs (needle-nose pliers, etc.) and heat it over a gas flame (stove is OK). When it
begins to sag (it looks sort of like a Cu bag containing molten Zn) touch it onto a collecting surface ( I used cured plaster). This ruptures the Cu
bag and gives you a blob of Zn. You are left holding the Cu (it's "crunchy" with oxide) "skin" with some residual Zn, and what looks like slag.
After this, do what you will with the Zn.
Cheers,
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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Magpie
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| Quote: |
Although dropping a penny into HCl solution would work easily, it seems that recovering anhydrous ZnCl2 may be troublesome.
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I have an old (1923) high school lab manual that says anhydrous ZnCl2 can be made as follows:
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1. Weigh out 2 grams of Zn and place in an erlenmeyer flask.
2. Add 10 mL of conc HCl and cover flask with a watch glass.
3. Place on ringstand with protective wire gauze pad and heat gently with a small flame (which does not touch the pad) until the zinc is dissolved.
4. Increase the flame and boil until the water is evaporated (bubbles practically stop).
5. Reduce the flame until it does not quite touch the pad and remove the watch glass. The zinc chloride will solidify and then melt. Just as soon
as it melts, stop heating.
Zinc chloride absorbs water from the air.
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To keep it water free I would cover it as soon as possible after it has melted. Or cover it with a dry gas and then cap it.
Note: For historical accuracy the manual specified an asbestos plate instead of a wire gauze pad (my words).
[Edited on 27-8-2008 by Magpie]
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ScienceSquirrel
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Zinc sheet is widely used as 'flashing' around skylights etc in Europe and maybe elsewhere.
A friendly roofer will probably donate you a piece of scrap for nothing.
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woelen
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This indeed is a nice source of zinc, but keep in mind that it is technical grade. If you dissolve such zinc in HCl (which works very well, even
better than pure zinc), then you get a rather nasty smell. I'm not sure about the nature of the smell, it might be due to phosphine and arsine or
related organic derivates thereof. Technical grade zinc may contain small amounts of P and/or As.
So, if you dissolve such technical grade zinc, please do that outside!
[Edited on 27-8-08 by woelen]
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smuv
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Also related to safety; avoid inhaling the fumes of any burning zinc (metal fume fever); That means watch out when you are trying the melt the metal
out of the pennies.
P.S. Ozone I like your method; I tried something similar but probably not as efficient; I cut the penny in half with tin snips and then heated each
half of the penny till it sagged and shook the penny over water. My method wasn't that efficient and only recovered ~60% of the zinc in the penny.
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zephram
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If you live near a boat yard an easy source of zinc could be disused corrosion protection anodes. Often they're thrown away with quite a bit of good
metal remaining. Drill into the anode to produce clean turnings.
I am not about the composition of marine anodes but those intended for fresh water use may contain more magnesium.
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MagicJigPipe
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I'm pretty sure that anhydrous ZnCl2 must be produced by Zn + HCl or Cl2 (I think Cl2 would be better because a) no hydrogen produced b) lower heat
needed). Every ZnCl2 (anhydrous) prep I've seen says to do this. I think it is damn near impossible to dehydrate ZnCl2 through simple heating.
Of course I could be wrong because I don't believe I've made it before... Or have I? I can't remember! Well, it obviously didn't stand out in my
mind if I did.
In the end I suppose it depends on what you are going to use it for. So? What are your plans for it?
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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