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gatewaycityca
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[*] posted on 22-2-2014 at 17:29
Making a battery with concentrated lemon juice?


I've been collecting a lot of lemons lately. I wanted to boil lemon juice down to evaporate excess water from it and hopefully have a stronger concentration of citric acid. Once reason is I wanted to experiment with baking soda and more concentrated lemon juice to get a stronger endothermic reaction. But now, I've been thinking...I know you can make a small (and very weak) battery from a lemon, and it could power things like a calculator, LEDs, etc. But what if I use concentrated lemon juice?

If I were to boil down a lot of lemon juice, to get it as concentrated as I can, how much power could I reasonably expect to get? And what would be the best (though common) metals to use for the electrodes? I'm not expecting a miracle - if I could get a sufficient voltage and current to maybe power a small DC motor, and maybe a light bulb, that would be plenty.

There are a ton of websites showing how to make batteries from lemons, and of course a lot of kids have done that for school. But I haven't heard or read about anyone trying it with highly concentrated lemon juice.
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[*] posted on 22-2-2014 at 18:56


Under these conditions, increasing the electrolyte concentration will not appreciably increase the voltage or current. You should do some reading up on electrochemistry. For starters, a table of standard electrode potentials will help:

http://hyperphysics.phy-astr.gsu.edu/hbase/tables/electpot.h...

Also,

https://en.wikipedia.org/wiki/Nernst_equation




As below, so above.
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[*] posted on 23-2-2014 at 06:20


@gatewaycityca:

Firstly google for it: it think there are plenty 'instructables' on this subject that will show you which reactions take place. CC is right that the voltage oobtained from such a battery doesn't vary that much with acid concentration. The lemon juice really acts as an aqueous conductor (electrolyte) but its conductivity doesn't depend much on citric acid concentration.

Edit: I see Wiki has a good entry on it.

@CC:

'gateway' is a total beginner. Just shoving the electrochemical series and the Nernst Equation under his nose won't significantly help him.

[Edited on 23-2-2014 by blogfast25]




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gatewaycityca
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[*] posted on 23-2-2014 at 21:15


Thank you for your help, but I'm still confused about why the concentration of citric acid wouldn't affect the output. So it's not the concentration of the acid, but only the type of acid which determines the output voltage and current capacity of a battery cell? I mean, I knew that obviously a battery with sulfuric acid or some other strong acid would be much more powerful than one using a weak acid like citric or acetic. But I thought that a stronger concentration would have a stronger chemical reaction and result in higher voltage. That's why I'm confused.

I kind of understood that table showing electrode potentials, showing which types of electrodes would have a higher potential difference. But I don't know how to read the formulas! I never studied chemistry in school when I was a kid, and I'm just now learning all this on my own. (Although I could just Google the formulas to see what materials they refer to).

[Edited on 2-24-2014 by gatewaycityca]

[Edited on 2-24-2014 by gatewaycityca]
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[*] posted on 24-2-2014 at 05:50


@gatewaycity:

Start here, especially the part on 'variations'.

http://en.wikipedia.org/wiki/Lemon_battery

Different pairs of metals do significantly affect the voltage but type and strength of electrolyte has little influence.




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gatewaycityca
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[*] posted on 24-2-2014 at 16:04


Thank you, Blogfast25. I actually looked that up on Wikipedia and I was reading that article. I think I'm starting to understand a little better now. So what actually generates an electric current in a battery is the reaction between the metals...basically one type of metal trying to draw ions from the other, with the electrolyte just working as a conductor? I always thought the way a battery worked was from the acid itself causing a chemical reaction and freeing electrons from the metal somehow as it broke down the metal plates or electrodes.

I have a LOT to learn!

But if the strength or type of electrolyte doesn't have much effect on the voltage, then why do large batteries like car batteries need such strong and toxic acids like sulfuric acid?
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Artemus Gordon
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[*] posted on 24-2-2014 at 18:05


Car batteries need to be rechargable, so the anode and cathode reactions need to both be able to run both forward and backward without generating gases, otherwise you would have to keep replenishing the lost atoms as the gas leaks away. Lead, lead oxide and sulfuric acid is one of the first combinations that accomplished this, and it works well enough that there hasn't been a big push to replace it. Other rechargable batteries can be made that use salts instead of acid for the electrolyte such as lithium-ion batteries.
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[*] posted on 25-2-2014 at 04:59


Quote: Originally posted by gatewaycityca  
So what actually generates an electric current in a battery is the reaction between the metals...basically one type of metal trying to draw ions from the other, ..


It isn't ions. It is electrons. One of the metals gets oxidized and the other gets reduced. In the case of zinc and copper, zinc gets oxidized

Zn -> Zn2+ + 2 e

and on the copper side, it would be some copper compound on the surface of the metal that gets reduced. Perhaps it is CuO, CuCO3, Cu(OH)2 or some kind of mixture called patina

Cu2+ + 2 e -> Cu




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[*] posted on 25-2-2014 at 05:33


Quote: Originally posted by vmelkon  
Quote: Originally posted by gatewaycityca  
So what actually generates an electric current in a battery is the reaction between the metals...basically one type of metal trying to draw ions from the other, ..


It isn't ions. It is electrons. One of the metals gets oxidized and the other gets reduced. In the case of zinc and copper, zinc gets oxidized

Zn -> Zn2+ + 2 e

and on the copper side, it would be some copper compound on the surface of the metal that gets reduced. Perhaps it is CuO, CuCO3, Cu(OH)2 or some kind of mixture called patina

Cu2+ + 2 e -> Cu


On copper side hydrogen ions are reduced to hydrogen gas, not copper ions (from the same wiki page).
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[*] posted on 25-2-2014 at 10:01


Quote: Originally posted by gatewaycityca  
But if the strength or type of electrolyte doesn't have much effect on the voltage, then why do large batteries like car batteries need such strong and toxic acids like sulfuric acid?


Car battery acid is ~30% concentration, so I wouldn't call it strong. I've spilled 20% acid on my hand a few times with no ill effects (washing it off within a minute or two, of course). I'd also hesitate to call it toxic, except in this case it would be contaminated with lead.

Artemus Gordon's comment is a good explanation.
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Zyklon-A
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[*] posted on 25-2-2014 at 10:16


Many people (including myself) have spilled ~98% H2SO4 on hands, arms, legs ect. without any chemical burns. Just wash it off quick enough (within one minute) and if possible dunk affected skin in in a basic solution.
I always keep a big jar full of NH3(aq) mixed with Na2CO3 for washing off acids. And I keep a jar full of household vinegar, for washing off basic substances.
Also, can we try to remember the definition of ACID STRENGTH?
[EDIT] Typo.

[Edited on 25-2-2014 by Zyklonb]




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gatewaycityca
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[*] posted on 25-2-2014 at 18:16
Preventing bacteria growth in concentrated lemon juice


Hi guys,

Thanks to everyone who has been helping with my questions lately. So I've been collecting and juicing a lot of lemons lately, and boiling the juice down to make it very concentrated. At the moment, I've just been storing it in a plastic 2-liter bottle and keeping it in the fridge. I've been concerned about the juice going "bad" and harboring bacteria. I wouldn't drink the stuff of course, but I'd still be worried about it being contaminated with bacteria and catching something from inhalation, etc.

My question is, would heavily concentrated lemon juice get so acidic that bacteria couldn't even grow in it anymore? I assume that by boiling the juice, that would kill anything that happened to be in it. But I'm hoping that I could store the concentration at room temperature and not have to keep it in the fridge anymore. Would that be safe? I want a container of strong citric acid solution for experiments, not a bacteria magnet. lol
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[*] posted on 25-2-2014 at 18:34


Boiling alone will not sterilize your juice. You need to autoclave it in a sealed vessel, if you don't have an autoclave a pressure cooker will work. Also its probably not going to harbor a lot of bacteria, that being said there are plenty of bacteria that can survive and thrive in low pH solutions (Pediococcus comes to mind). I think molds can tolerate low pH as well, but im not sure.

If you can't sterilize with heat you may consider adding some metabisulfite salt, brewers and winemakers use those to kill spoilage microorganisms before pitching yeasts.
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[*] posted on 25-2-2014 at 19:22


You can just place the vial in a water bath in a pressure cooker, as mnick12 alluded to. If you don't have one in your kitchen, you can get "no name" brand ones from your cheapo stores like Wallmart, I assume.
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[*] posted on 26-2-2014 at 02:07


Quote: Originally posted by papaya  
Quote: Originally posted by vmelkon  
Quote: Originally posted by gatewaycityca  
So what actually generates an electric current in a battery is the reaction between the metals...basically one type of metal trying to draw ions from the other, ..


It isn't ions. It is electrons. One of the metals gets oxidized and the other gets reduced. In the case of zinc and copper, zinc gets oxidized

Zn -> Zn2+ + 2 e

and on the copper side, it would be some copper compound on the surface of the metal that gets reduced. Perhaps it is CuO, CuCO3, Cu(OH)2 or some kind of mixture called patina

Cu2+ + 2 e -> Cu


On copper side hydrogen ions are reduced to hydrogen gas, not copper ions (from the same wiki page).


Now I have question related to my own answer: if the copper side stays "inert", so copper ions don't participate(read that wiki page), then what will be the potential if I take a battery with the copper electrode paired with even more inert metal like Ag, or graphite? (Cu-Ag and Cu-C). In theory it must be 0V, is this the case?
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[*] posted on 26-2-2014 at 03:11


i would be more concerned about fungi than bacteria, and agree with them that autoclaving is the best option.
However if you cant autoclave it, you could always try using tyndallization although its somewhat of a hassle and not as effective as autoclaving, or pasturizing it, which isnt as effective as tyndallizstion

http://en.wikipedia.org/wiki/Tyndallization

http://en.wikipedia.org/wiki/Pasteurization
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[*] posted on 26-2-2014 at 03:21


The only thing (except for some very thermophilic archaea) that will survive 100 degrees Celcius are spores, but if you boil twice with 24-48 hours in between the spores will get the change to germinate and get killed during the second boil.


[Edited on 26-2-2014 by Tsjerk]

[Edited on 26-2-2014 by Tsjerk]
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[*] posted on 26-2-2014 at 03:24


Well if pasteurization is an option, you can just use your dishwasher on the longest/hottest settings for that. I do that to kill yeast once bottle carbonation is high enough in sweet ciders so they stay sweet/don't explode.
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[*] posted on 26-2-2014 at 03:29


Quote: Originally posted by gatewaycityca  
Thank you, Blogfast25. I actually looked that up on Wikipedia and I was reading that article. I think I'm starting to understand a little better now. So what actually generates an electric current in a battery is the reaction between the metals...basically one type of metal trying to draw ions from the other, with the electrolyte just working as a conductor? I always thought the way a battery worked was from the acid itself causing a chemical reaction and freeing electrons from the metal somehow as it broke down the metal plates or electrodes.

I have a LOT to learn!

But if the strength or type of electrolyte doesn't have much effect on the voltage, then why do large batteries like car batteries need such strong and toxic acids like sulfuric acid?

What nobody seems to have mentioned is that unlike in most batteries, in lead-acid batteries the sulfuric acid does take part in the reaction, serving as more than just an electrolyte. This is why relatively concentrated sulfuric acid is necessary for a lead-acid battery to work.
IIRC, the reactions are:
Anode: Pb + SO42- -> PbSO4 + 2e-
Cathode: PbO2 + SO42- + 4H+ + 2e- -> PbSO4 + 2H2O




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[*] posted on 26-2-2014 at 03:32


That probably works because your yeast already out-selected every other kind of organism, but is not able to form spores itself.

The problem here is that there are more than likely a lot of spores in the juice, even more than likely also from Aspergillus strains, of which some have a pH optimum as low as 2!

[Edited on 26-2-2014 by Tsjerk]
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[*] posted on 26-2-2014 at 04:19


Add some lime juice.
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[*] posted on 26-2-2014 at 04:21


And that would work because?
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26-2-2014 at 04:50
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[*] posted on 27-2-2014 at 15:15


I don't know enough biochemistry to explain how it works, sorry.
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[*] posted on 28-2-2014 at 07:12


Could you tell where you got this information from? There are a lot of antimicrobial compounds in citrus fruits in general (especially the skin), but they are already in the juice as it is lemon juice to start of with. That is the only reason I could imaging.

Besides that, both bacteria and fungi have a wide range of susceptibility/resistance against different compounds, so the change of finding a microbe capable of growing on lemon/lime juice in the flask is quite big. I ones saw a fungus growing on 50% ethanol with pretty high copper and azide concentrations, I believe there is a nice threat about organisms growing in unusual places on this forum somewhere.

Nice example I was just reading: ''Genetic Basis for Daptomycin Resistance in Enterococci (Antimicrob Agents Chemother. Jul 2011).'' Where they manage to get a susceptible Enterococcus strain daptomycin resistant with a MIC>256 ug/ml, whereas the highest clinical resistance found until publication was only 8 ug/ml (in just 12 days!).

[Edited on 28-2-2014 by Tsjerk]
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shocked.gif posted on 5-3-2014 at 14:23


Quote:
I ones saw a fungus growing on 50% ethanol with pretty high copper and azide concentrations

...

are you even serious




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