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| Salmon Egg... |
 Posted: Wed Nov 04, 2009 11:54 pm |
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Please excuse me if this is a repost. I did not see it on the group
site. There also were no responses that I could see. I think this is an
interesting aspect of chemistry--but I have been wrong before.
I have gotten interested in the history of electric telegraph. The
primary cell of choice well into the 20th century seems to be the Zn
anode, Cu cathode gravity cell. See Wikipedia among others. As far as I
can tell, during proper operation sulfuric acid in the electrolyte is
not used up. Zinc gets dissolved while copper gets plated out. This
copper plating frees up sulfate ion to move up from the bottom of the
cell to the top in order to maintain charge balance with the newly
created zinc ion. This leads me to a number of questions.
The advantage of the gravity cell is that no gas was evolved. That is
no hydrogen bubbles coated the cathode in a way that would increase
internal resistance. Additionally, using gravity to separate the
solutions removed the necessity of porous separators that would clog up
and give trouble.
1. What is the role of the sulfuric acid? Is it used to control pH.
2. Why does the pH need to be controlled. Is it to prevent
precipitation of Zn and Cu hydroxides?
3. What is the proper pH.
4. Is the pH uniform in the copper and zinc solutions? That is, are the
hydrogen (hydronium) ion able to move freely between the top and bottom?
5. I can understand why you would not want copper ion to reach and
plate out on the zinc anode. Does that depend primarily on gravity
between refurbishments of the cell? Is current flow significant in
keeping copper on the bottom?
6. What harm, if any, would there be if zinc ion moved into the copper
solution?
I have other questions as well. I am trying to understand some of these
details in order to improve my understanding of chemistry.
Bill
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As the years go by, dying just before having to fill out a tax return has merit. |
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| dlzc... |
| Posted: Thu Nov 05, 2009 8:11 am |
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Dear Salmon Egg:
On Nov 4, 9:54 pm, Salmon Egg <Salmon... at (no spam) sbcglobal.net> wrote:
[quote]Please excuse me if this is a repost. I did not see
it on the group site. There also were no responses
that I could see. I think this is an interesting aspect
of chemistry--but I have been wrong before.
[/quote]
It is still there. And may be mistaken, but never wr... wr...
incorrect.
The spammers have started flooding most / all the unmoderated
newsgroups in order to avoid paying for advertising, and Google.Groups
allows them to post without any sort of "spam checking". So it got
buried.
....
[quote]6. What harm, if any, would there be if zinc ion
moved into the copper solution?
I have other questions as well. I am trying to
understand some of these details in order to
improve my understanding of chemistry.
[/quote]
A sidelight, there are refrigeration cycles that depend on gravity to
operate, do not use electrically-powered compressors, but use a flame
to drive the process. Pretty common in mobile homes...
I suspect your process will shut down if there is significant mixing,
that the sulfuric acid (or what it dissociates into) is a catalyst /
transport actor, and that given time (and a cessation of mixing) the
process will restart after stratification re-establishes.
David A. Smith |
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| Michael Moroney... |
| Posted: Thu Nov 05, 2009 1:28 pm |
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Salmon Egg <SalmonEgg at (no spam) sbcglobal.net> writes:
[quote]I have gotten interested in the history of electric telegraph. The
primary cell of choice well into the 20th century seems to be the Zn
anode, Cu cathode gravity cell. See Wikipedia among others. As far as I
can tell, during proper operation sulfuric acid in the electrolyte is
not used up. Zinc gets dissolved while copper gets plated out. This
copper plating frees up sulfate ion to move up from the bottom of the
cell to the top in order to maintain charge balance with the newly
created zinc ion. This leads me to a number of questions.
[/quote]
You may want to use Google to find "gravity cell" or "crowfoot batterty".
[quote]3. What is the proper pH.
[/quote]
One site (http://chss.montclair.edu/~pererat/mbatt.htm) mentions the
proper amount of sulfuric acid is one teaspoon per container (6" diameter
x 8" high). Someone can calculate the pH from that.
[quote]5. I can understand why you would not want copper ion to reach and
plate out on the zinc anode. Does that depend primarily on gravity
between refurbishments of the cell? Is current flow significant in
keeping copper on the bottom?
[/quote]
Copper is pretty dense, it's not about to float in water or CuSO4 solution.
The website mentioned mentions current flow prevents diffusion of the
CuSO4 and the ZnSO4 solutions.
[quote]6. What harm, if any, would there be if zinc ion moved into the copper
solution?
[/quote]
Probably reduced voltage. Apparently these batteries have to be "started"
by short-circuiting them for 24 hours. |
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| Salmon Egg... |
| Posted: Thu Nov 05, 2009 9:28 pm |
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Guest
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In article <hcvn2f$oc1$1 at (no spam) pcls6.std.com>,
moroney at (no spam) world.std.spaamtrap.com (Michael Moroney) wrote:
[quote]Copper is pretty dense, it's not about to float in water or CuSO4 solution.
The website mentioned mentions current flow prevents diffusion of the
CuSO4 and the ZnSO4 solutions.
6. What harm, if any, would there be if zinc ion moved into the copper
solution?
Probably reduced voltage. Apparently these batteries have to be "started"
by short-circuiting them for 24 hours.
[/quote]
Thank you for the reply. I probably should have used the term "copper
ion" in my post rather than "copper." I realize that copper metal will
not float.
I find your site reference interesting althouh I did not read it in
detail yet.
The complement to spam is data overload. Googl searches often provide
thousands of hit. Much is relevant. Even more is irrelevant, so that
even legitimate information needs to be sorted through to get to the
crux of a subject. That is why a post like yours is helpful.
Bill
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As the years go by, dying just before having to fill out a tax return has merit. |
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| Michael Moroney... |
| Posted: Fri Nov 06, 2009 8:33 am |
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Guest
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Salmon Egg <SalmonEgg at (no spam) sbcglobal.net> writes:
[quote]The complement to spam is data overload. Googl searches often provide
thousands of hit. Much is relevant. Even more is irrelevant, so that
even legitimate information needs to be sorted through to get to the
crux of a subject. That is why a post like yours is helpful.
[/quote]
The trick is knowing how to use Google, to use enough of the right
keywords to find what I want. I just entered "telegraph battery copper
zinc" (without quotes) and the site I mentioned was the first hit. Seeing
a word that I could/should have used as a keyword ("gravity") in the title
but didn't, as well as some technical discussion in what Google returned
told me that it was likely a useful hit. I didn't look at the other hits
to see if they were useful, except one other, which was a scanned, very
old book, which might have useful info. |
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