Recently at home we did the old lemon battery experiment: stick copper electrodes and zinc-coated electrodes into a lemon to power an LED. (Actually four lemons in series: the voltage from a single lemon was not high enough to power our LED.)

Zinc metal is more reactive than hydrogen and this can be viewed as a displacement reaction. There is an excess of hydronium ions balancing the citrate anions (and some other anions): afterwards, some of the zinc has entered soluton as zinc cations, and some hydrogen gas has appeared at the copper electrode.

This got me thinking about Volta’s original battery, the zinc-copper pile. He used disks of cardboard soaked in brine, which is mainly a sodium carbonate solution.

Now, sodium is the main cation in the original solution. Zinc is less reactive than sodium so it cannot displace it. So what is the reaction?

The only thing I can think is that hydrogen is still being displaced and the only thing that the sodium chloride is doing is aiding the carriage of charge. But in a sodium chloride solution there are no more hydronium ions than there are in pure water: less than one part in a million, equal in number to the hydroxide ions. As the hydrogen is depleted, I would expect a build up of hydroxide ions: effectively, zinc hydroxide is being added to the solution, and it becomes more basic.

If I am right, these brine piles should have had much lower current than if acids were used.

Is my analysis correct?

Sounds good to me. Except that the salt is also acting as a buffer, stabilising the pH of the electrolyte so it’s not affected as much by those metal hydroxides you mentioned.

But I Am Not A Chemist.

Well now I am not a chemist either but sodium chloride ain’t much chop as a buffer solution because sodium is well soluble with all the anions here and chloride is well soluble with all the cations here…

On the other hand zinc hydroxide is only a bit soluble so there will be a lid on how basic the solution can become.

The brine batteries were replaced by acid batteries (and some other electrolytes involving not-very reactive metals) as the early 19th century wore on. Interestingly Volta had a completely erroneous idea about the cause of the electricity, and did not believe that zinc metal was consumed by the process.

As I understood it acid is needed to attack the metal to allow current to flow more effectively , brine is simply a good conductor of current than causing the metals to be anodes/ cathodes.

As the metal is eaten away it releases electrons from the anode

Unless someone can explain how it really works. We are told about dissimilar metals in an electrode but rarely told about exactly how this works – it’s just a known fact that most people know without knowing the mechanism.

An acid based electrolyte would be better than just an electrolyte based on something like salt , I couldn’t think when I’ve ever seen any experiment where the electrodes are dipped into an alkaline mix ( rather than acid )

The last post has words auto corrected by iPhone

what happened to carbonate

SCIENCE said:

what happened to carbonate

Perhaps you could rephrase.

brine, which is mainly a sodium carbonate

SCIENCE said:

brine, which is mainly a sodium carbonate

What? No.

yes…

it got a bit confusing

but this chap assures us it is

tokyo3.org/forums/holiday/posts/625024/

Anyway, what I was saying was, it’s quite a good idea, perhaps the acid is carbonic acid from the students breathing on the setup.

SCIENCE said:

yes…

it got a bit confusing

but this chap assures us it is

tokyo3.org/forums/holiday/posts/625024/

I’m not even going to read that. Carbonate is not the major component of brine. The main cation is sodium: the main anion is chloride. The second major anion is sulphate. The third major anion is bromide. Depending on the exact source the abundance of carbonate will vary but it is going to be about 1/1000 of the chloride abundance.

You got salts and you’ve got salt that we know

Salts are a metal combined with a non metal , presumably that can dissolve ( can’t remember the entire definition)

dv said:

SCIENCE said:

yes…

it got a bit confusing

but this chap assures us it is

tokyo3.org/forums/holiday/posts/625024/

I’m not even going to read that. Carbonate is not the major component of brine. The main cation is sodium: the main anion is chloride. The second major anion is sulphate. The third major anion is bromide. Depending on the exact source the abundance of carbonate will vary but it is going to be about 1/1000 of the chloride abundance.

Ummm.. It’s your post dv!

I see now that SCIENCE is pointing out a braino that I made in the first post.

Unfortunately there’s no Edit function so it will remain forever a monument to hubris and a fitting and constant invitation to humility.

dv said:

I see now that SCIENCE is pointing out a braino that I made in the first post.

Unfortunately there’s no Edit function so it will remain forever a monument to hubris and a fitting and constant invitation to humility.

lol, pity another few on here were as graciouis when wrong.

jjjust moi said:

dv said:

I see now that SCIENCE is pointing out a braino that I made in the first post.

Unfortunately there’s no Edit function so it will remain forever a monument to hubris and a fitting and constant invitation to humility.

lol, pity another few on here were as graciouis when wrong.

when it happens, I’ll give it a try too.

dv said:

I see now that SCIENCE is pointing out a braino that I made in the first post.

Unfortunately there’s no Edit function so it will remain forever a monument to hubris and a fitting and constant invitation to humility.

dv said:

I see now that SCIENCE is pointing out a braino that I made in the first post.

Unfortunately there’s no Edit function so it will remain forever a monument to hubris and a fitting and constant invitation to humility.

Since you also talked about sodium chloride I suppose there is at least a 50% chance it was a case of just typing the wrong word, rather than total ignorance of basic chemistry.

The Rev Dodgson said:

Since you also talked about sodium chloride I suppose there is at least a 50% chance it was a case of just typing the wrong word, rather than total ignorance of basic chemistry.

ROFL thanks for that.