Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: bmore_ravens on 14/08/2012 08:27:05
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I want to use electrolysis of salt in water to make sodium hydroxide
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Interesting idea. Keep in mind that the electrolysis of salt water will also produce chlorine gas, so make sure it is well vented.
You can, of course, buy NaOH or KOH, commonly sold as drain cleaners.
You should find carbon electrodes at a welding shop (carbon arc cutting). Also, you might be able to take the electrodes out of old alkaline batteries (C or D cells, or even larger batteries).
I found this up in the woods last year.
http://www.thenakedscientists.com/forum/index.php?topic=2178.msg367910#msg367910
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.thenakedscientists.com%2Fforum%2Findex.php%3Faction%3Ddlattach%3Btopic%3D2178.0%3Battach%3D15285%3Bimage&hash=d9c65cb48baa6fe294d82fbac5f07e16)
My best guess was that it was an electrode out of a large electric lantern battery, or perhaps even a telegraph battery.
Oops, I'm seeing the battery electrodes may be manganese dioxide doped with carbon. But, they may still work for your needs.
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From CliffordK
Oops, I'm seeing the battery electrodes may be manganese dioxide doped with carbon. But, they may still work for your needs.
Yes, I think that where your answer might be slightly out is in your stipulation of alkaline batteries. I know that the original dry cells with zinc and ammonium chloride paste did have graphite electrodes 40 years ago, and that we used to demolish them and use them quite successfully for amateur schoolboy electrolysis experiments.
Manganese dioxide is not, by the way an inert material in an electrode. It is a strong oxidant, and the electron sink in the dry cell chemical reaction:
http://en.wikipedia.org/wiki/Zinc–carbon_battery
Note though that the manganese dioxide is in a paste surrounding the anode, which is a simple graphite rod.
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Thanks, now I just need to find a welding shop.
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Work it out with a pencil ? ... https://en.wikipedia.org/wiki/Graphite#Pencils
(burn away the wood to leave the graphite core ?)
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Work it out with a pencil ? ... https://en.wikipedia.org/wiki/Graphite#Pencils
(burn away the wood to leave the graphite core ?)
Pencils leads are a graphite/clay mix. But, they still might work.
If you go to an art supply shop, you can buy carbon for painting. It crumbles quite easily, but it can be purchased in larger pieces, and might be worth trying.
Any chance of snagging the electrode out of a WWII anti-aircraft carbon arc lamp?
Carbon fiber, such as a carbon fiber fishing pole would have carbon fiber and a resin. However, you could also find the raw carbon fiber cloth which would be great for a large surface area electrode.
As William mentioned, if you use a metal tank, it can be used as one electrode too. Or, if you like graphite, you can find graphite crucibles. The larger ones can be quite expensive though.
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Oops,
I see the welding carbon arc cutting electrodes may be copper clad which may not be what you intended.
These carbon arc electrodes on E-bay are HUGE.
http://www.ebay.com/itm/2-CARBON-ARC-ELECTRODES-15-16-BY-12-INCH-rod-/330752317892?pt=LH_DefaultDomain_0&hash=item4d025fd9c4
About an inch in diameter by a foot long.
I see I get an interesting variety of electrodes searching for "Carbon Electrode".
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Thank you for the ideas, I'm probably going to get the ones from ebay.
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William really this is once again utter garbage and irrelevant garbage. Yes marble can effectively transmit ultra high frequency AC electricity. Yes marble has a finite non-zero conductance for the DC electricity that is needed for an electrolysis reaction, or at least for the type of electrolysis that the original poster was seeking to set up. But no, marble cannot make a suitable electrode for such a reaction because of its minutely low conductivity. And why do you always adorn your postings with totally irrelevant links and diagrams?
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Work it out with a pencil ? ... https://en.wikipedia.org/wiki/Graphite#Pencils
(burn away the wood to leave the graphite core ?)
Pencils leads are a graphite/clay mix. But, they still might work.
I forgot about mechanical pencil "leads" ...
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So the mechanical pencil leads would work for what I'm trying to do, right?
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So the mechanical pencil leads would work for what I'm trying to do, right?
The mechanical pencil "leads" are made of graphite, (not lead), evidently can be used as electrodes (https://www.youtube.com/watch?v=tvxSgbIelYk).
https://en.wikipedia.org/wiki/Electrolysis_of_brine#Membrane_cell
The products of this reaction are all hazardous:-
chlorine gas is poisonous, hydrogen gas is flammable and sodium hydroxide is caustic (https://en.wikipedia.org/wiki/Sodium_hydroxide#Safety).
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I know what the electrolysis will produce, but I'm doing it outside and wearing a gas mask so I should be alright. Thank you for your concern though.
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Dielectrics conduct electricity the fastest of all, but at reduced current.
Sincerely,
William McCormick
So you have chosen to carry on talking bollocks then.
Anyway, back at the topic,
I used to get the carbon rods out of old batteries- but it's messy.
http://www.youtube.com/watch?v=oN21ELKEIns (http://www.youtube.com/watch?v=oN21ELKEIns)
Pencil leads will do the job.
I doubt that you will get enough chlorine or hydrogen to do any harm but working outside isn't a bad idea.
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Good point that brushes might be another source of high carbon electrodes.
They generally aren't too long. But, you could take some out of an old electric motor. Or, perhaps purchase new ones. Our local building supply store sells a few.
Many spark plug wires also have high carbon filaments. Strip back a little insulation, and they might be easy to use.
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Well, there are a few sources of carbon electrodes. Pencil leads work, but they are a bit small.
The carbon rods from batteries are a good size and free which is nice- but getting them can be messy.
You can buy carbon rods from welding suppliers and strip the copper coating off them (that's what I usually do- but it depends on having a suitable etchant).
You can use carbon brushes though they aren't usually a very convenient shape or size (they might be free if you know somewhere that scraps electric motors.)
I think the electrical resistance of spark plug leads would be a problem.
Of course, if you live on the same planet as Mr McCormick, the resistance won't matter and you can use anything you like.
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When you get your electrode, Bmore, you may still have quite a lot of difficulty with the practical aspects of this electrolysis. It is an industrial method for producing caustic soda and chlorine gas known as the "chloralkali process". But it is not easily adapted for home, or even laboratory use,
An efficient electrolysis cell depends on a large electrode surface area and a small electrode gap. But the gap must be large enough to prevent the gases being evolved at the electrodes reacting with one another. Hydrogen gas and chlorine gas will react together quite readily, and give off a lot of heat when they do. The reaction is likely to start "spontaneously" because it is triggered by visible light. The gases need to be separately collected as they bubble off, and channelled apart.
With any of the electrode materials that have been suggested you will be lucky to get a resistance below 100 ohm in your brine-filled cell. That would mean a current of 0.1 amp for a 10 volt DC supply.
The overall reaction 2 NaCl + 2 H2O --> H2 + Cl2 + 2 NaOH requires 2 mol of electrons (roughly 200,000 coulomb) to produce 2 mol of NaOH (= 80 gram). 200,000 coulomb at 0.1 amp would mean 2,000,000 seconds of current flow to produce 80 gram of NaOH, or {25,000 seconds = 7 hours} per gram.
Then there is the problem of product separation. It is not possible to run this reaction until all, or even most of the sodium chloride is gone, because the hydrogen/oxygen electrolysis is always lurking in the background as a competitive electrolysis reaction, and will take over if the chloride concentration falls even a little. Separating sodium hydroxide from sodium chloride and water is a very difficult task.
Good luck with your explorations, but I think you are embarking on a path that you will find very frustrating.
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You may also choose to look up making lye from wood ash. There should be lots of notes about it on the internet.
I think I mentioned earlier that carbon fiber mesh would give you rather good surface area, although you may need some kind of structure to separate the cathode and anode.
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I have many glass tube and jars I could use to contain the gaseous by products, but should I want to dispose of them, what would be the safest way to do so?
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I have many glass tube and jars I could use to contain the gaseous by products, but should I want to dispose of them, what would be the safest way to do so?
How much are you planning to make? A few grams?
Capture the hydrogen for "experiments", maybe in a mylar balloon.
Will the oxygen and chlorine come out together?
I suggested in another topic that you might try reacting your products to make HCl.
Otherwise, for very small test quantities, just let the gases escape (outside, or out a fume system).
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I will also mention that electricity has a wonderful ability to find the path of least resistance, be that the metal your are welding connected to your grounding cable, or through your body.
I find it amazing that a person can generally hold a piece of filler wire in the arc with one's bare hands and not get shocked. But, your work is generally well grounded, so it is the path of least resistance. You, on the other hand generally you are not well grounded. Even touching the grounded work, your body still isn't the path of least resistance.
When you weld your filler wire to the tungsten electrode, away from the work, then I presume most good welders would drop the power output, and you still may not be grounded.
The problem may occur with one piece of metal that is well grounded, and one that is not, and you in the middle. Or, the use of a grounded welding table instead of grounding your work, coupled with variable output from your power supply.
Anyway, at this point, we need to get back onto the original topic of carbon electrodes NaOH.
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I know what the electrolysis will produce, but I'm doing it outside and wearing a gas mask so I should be alright. Thank you for your concern though.
Do you really need salt in the electrolysis reaction? If not sodium bicarbonate (baking soda), I don't think, will produce any harmful gases. However, I am not sure that this will produce sodium hydroxide. If you have access to it, you can put some elemental sodium in water and this will produce sodium hydroxide. Be careful, though, as this is quite an explosive reaction-even a small piece of sodium will produce a powerful explosion-small pieces of glowing material may be shot into the air.
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I know what the electrolysis will produce, but I'm doing it outside and wearing a gas mask so I should be alright. Thank you for your concern though.
Do you really need salt as your catalyst in the electrolysis reaction? If not sodium bicarbonate (baking soda), I don't think, will produce any harmful gases. However, I not sure that this will produce sodium hydroxide however. If you have access to it, you put some elemental sodium in water and this will produce sodium hydroxide. Be careful, though, as this is quite an explosive reaction-even a small piece of sodium will produce an explosive reaction; small pieces of glowing material may be shot into the air.
(1) Lab Rat elemental sodium is much more dangerous and much less accessible than caustic soda, which can be readily bought at appropriate stores (hardware stores in this country; do not know what British/North American equivalents are). If the aim is simply to get hold of some caustic soda, there is no need for electrolysis or any other awkward and dangerous chemical procedure, and certainly not to use an extremely dangerous material like metallic sodium. In my student days there was a man at my university who had permanent lifetime employment as a "cleaner" because he had been blinded and had bad facial scars from an accident where water had come in contact with NaK eutectic that was being used as a coolant in some particle physics equipment.
(2) Salt is not a catalyst in this electrolysis reaction, it is a reactant, along with water. The stoichiometric form of the electrolysis reaction is
NaCl + H2O (+ electrical energy) --> NaOH + 1/2 H2 + 1/2 Cl2
The interfering reaction is simply
H2O (+ electrical energy) --> H2 + 1/2 O2
Under standard conditions (1.0 M chloride solution), the first reaction actually requires a higher electrical energy input than the second (E0 = 1.358 volt and 1.223 volt respectively), and so it is only kinetic factors that help the higher energy reaction to proceed -- probably preferential adsorption of chloride ions onto a fairly hydrophobic electrode (another good reason for using graphite). It is therefore essential to keep the chloride concentration high, well over 1 M. Probably the best way of achieving this is to have an excess of solid salt at the bottom of the cell that can dissolve to replace the salt that is being consumed.
From CliffordK:
Capture the hydrogen for "experiments", maybe in a mylar balloon.
Will the oxygen and chlorine come out together?
Yes they will come out together. That will not matter too much as a mixture of chlorine and oxygen gases is quite stable, but the mixture is much more dangerous in contact with hydrogen gas than either chlorine gas or oxygen gas alone would be.
I repeat that
When you get your electrode, Bmore, you may still have quite a lot of difficulty with the practical aspects of this electrolysis. It is an industrial method for producing caustic soda and chlorine gas known as the "chloralkali process". But it is not easily adapted for home, or even laboratory use,
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(1) Lab Rat elemental sodium is much more dangerous and much less accessible than caustic soda, which can be readily bought at appropriate stores (hardware stores in this country; do not know what British/North American equivalents are). If the aim is simply to get hold of some caustic soda, there is no need for electrolysis or any other awkward and dangerous chemical procedure, and certainly not to use an extremely dangerous material like metallic sodium. In my student days there was a man at my university who had permanent lifetime employment as a "cleaner" because he had been blinded and had bad facial scars from an accident where water had come in contact with NaK eutectic that was being used as a coolant in some particle physics equipment.
(2) Salt is not a catalyst in this electrolysis reaction, it is a reactant, along with water.
As for #1, I did warn that it was a dangerous reaction that would shoot off glowing debris. The second one, however, was my mistake.