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Author: Subject: NaOH
Saerynide
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NaOH

I made NaOH by electrolysing salt water and I trapped some of the Cl2 with an inverted test tube to make sure it was really working (I acciddently pulled up the test tube and inhaled the Cl2... so smart of me ). Anyways, I used carbon electrodes cause I figured the Na+ wouldnt plate it and I thought that Cl-/Cl2, H+ or OH- wouldnt attack carbon very easily.

Well I left it on for about 10 hours and when I came back, the solution was like grey with carbon dust settled all over the bottom. I left it for another 12 hours and my anode didnt look like the anode I had originally put in anymore I was on the verge of disintegrating. So Im guessing the Cl2 attacked it?

But what REALLY puzzles me is my cathode. The part of it above the level of the solution, is coated in what looks like a salt and carbon! And this trail of "stuff" contiues to run up my cathode about 3 inches out of the solution! Why would the carbon end up on the cathode unless it got ionized by the Cl2 formed at the anode? But carbon doesnt even ionize easily... Im really confused now.

Btw, Im new to this so please correct me if I say something totally stupid

[Edited on 17-11-2003 by Saerynide]

[Edited on 18-11-2003 by Saerynide]
Blind Angel
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The Electrode that "melted" is absolutly normal, it's actually how plating work. you put the anode in a metal and the other electrode is what you want to plate, the anode (-) will melt and stick to the cathode (+), the dark thing you have in you solution is elemental carbon i think.

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Saerynide
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Thats one thing cleared up, But I still dont get how the salt ended up on the cathode.

If the NaCl dissassociated into Na+ and Cl-, why would salt still run up my cathode?

And is there a better alternative for electrodes instead of carbon? I rather have my solutions stay colorless and contaminationless.
DDTea
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If you feeling like paying a bit of money, Platinum makes great electrodes. You can get 10 cm of 16 gauge Platinum wire for $80-$110. Check with your local jewelry store for their prices on Platinum wire.
vulture
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Platinum coated titanium is much cheaper and as indestructable as normal platinum. Also, you get much more surface area for a lower price.

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YOu cannot electroplate wih carbon in the same way as you can with (for example) copper. The copper is carries through the solution as Cu++ ions.
You can't get a carbon ion in solution in water.
The anode falls apart because of the mechanical action of the bubbles (the rate of attack by Cl2 or O2 is small at anything like normal temperatures.)
The stuff found at the cathode might be anything. It might be salt crystalising from a saturated solution or it might be some impurity from somewhere.
Saerynide
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Platinum wires... thats pricey. Does gold work? Its prety low on the reactivity series and its much more easily available...
Marvin
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Carbon electrodes will oxidise slowly. The oxidation is catalysed by OH-, and increases with increasing temperature (and therfore increasing current density). Carbon rods from batteries are the worst and the liquid while the cell is running will usually turn black from the very fine carbon.

If the solution is hot, and I suspect it was very hot, and the carbon electrodes get hot, it can crystalise on them, draw more of the black liquid up by capillery action and the setup ends up looking just like you've described. When the crystals dry it only takes a very small amount of carbon to make it look very dark.

Platinum wire is good for low current applications, for high, platinum plated electrodes are much better as vulture says. Platinum does dissolve very very slowly though. Id expect gold to dissolve more quickly in chloride cells.

Carbon gouging rods are pretty cheep, and if you use a lot of them together the current density will be so small much less total wear will happen, so this is an option. Keeping apart the anode and cathode compartments is a good idea to prevent the pH next to the anode from rising too high. A decent diaphram for home use I have yet to find.
Saerynide
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Ah finally the carbon issue has been sorted out and it can stop bugging me now. Thanks alot guys

Anyother thing just came to mind:

At the begining, i said i caught some Cl2 using an inverted testtube. Well, I tried to keep some (more like alot cause I used a HUGE testtube) of it just for the heck of it. I wondered how I could un-invert the test tube without dumping all the gas out. So I dropped a hunk of plasticine (I didnt have a stopper) into the solution and shoved the mouth of the test tube on it and took out the testube. That worked, and I left the tube outside in the garage.

Its been a few days and most of the Cl2 in the tube seems to have dissappeared. The contents of the tube isnt greenish anymore and plasticine on the inside seems to be corroding...

Is there a way to store Cl2 without it being all lost from reactions with the container/stopper?
Saerynide
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I decided to make another batch of sodium hydroxide, but this time, I seem to have gotten bleach or something...

I filtered out the solution many many times until there was no trace of carbon on the filter papers, but the solution is clearly yellowish (like bleach). It also smells like bleach... So could it be NaClO? And if it was, how could I ensure I only get NaOH and not NaClO?
Marvin
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If you allow the solutions around both electrodes to mix, you will get bleach. You will always get a small amount, its just something extra that needs to be removed during fractional crystalisation.

Chlorine will react with virtually everything you try to keep it in, if you wanted to keep a sample, youd probably have to use a glass ampule and seal it by melting the glass pipe. If the chlorine was dry it would probably keep indefinatly.
Saerynide
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How come bleach forms when the solutions around the electrodes mix?

Is it because some of the oxidized Cl- reacts with the OH- at the anode to form ClO- before it can combine into diatomic chlorine gas?
Theoretic
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Nah, it's the actual molecular chlorine disproportionating into Cl- and ClO- in a reaction with hydroxide ions:
Cl2 + 2OH- => Cl- + ClO- + H2O.
Chlorine atoms don't live that long.
BromicAcid
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So the some of the chlorine being generated will go into solution being in the mixture of:
Cl2 + H20 ----> HCl + HClO
Then the two of them will react with the hydroxide making sodium chloride and sodium hypochlorite in solution if it is cold, but if it is a bit warmer it will react according to:
3Cl2(aq) + 6NaOH(aq) -----> NaClO3(aq) + 5NaCl(s) + 3H2O(l)
The sodium chloride which is less soluble then the sodium chlorate will precipitate to an appreciable extent if the reaction continues.

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Saerynide
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Ooooh I see. Will setting the voltage higher and leaving it to run longer eventually break up the NaClO3 and leave only behing pure NaOH and water? Or is chlorate inevitable?
BromicAcid
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The production of chlorate is dependent on the temperature and on mixing of the products from the electrodes. So, keep the mixture cool, around 20 C or less and since you're trying to get sodium hydroxide either put some sort of membrane in place to prevent chlorine from mixing with the hydroxide solution or just don't disturb it so mixing will be minimal. It's not the electrolytic process producing the chlorate, it is the reaction between the chlorine gas and the hydroxide.

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Hermes_Trismegistus
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As a side note....the "carbon" rods you get from batteries are shite.

Might I suggest investing in a more sizable chunk of well bonded graphite from either a general materials supplier, or if you are willing to pay a couple bucks then look at glassblowing suppliers.

either way expect to pay a bit for it, but hey..

better than that cheap crumbly crap out of batteries, or getting the "leads" from pencils

the graphite in pencils has a sort of epoxy to aid bonding

graphite blocks for glassblowing are pretty pure and bonded under VERY high pressures

you can saw it but with small tooth saws and slowly, gently and easily so you don't produce cracks.

May be you might ask a glassblowing supply if they have cracked graphite paddles (sometimes they crack in shipping)

You could then cut some amazing, large and robust electrodes.

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Saerynide
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I wish I had access to all sorts of materials I need for stuff, but unfortunately thats not the case I have to make do with what's around the house or with what I can buy easily/cheaply. Im only in a junior in highschool, so I cant exactly try to order chemicals or afford to waste so much allowance on platinum wires

Btw, I used solid graphite (except for the outside coating) art pencils for my electrodes. They hold pretty well for hours if you keep a large part of it wrapped in electrician's tape.
Hermes_Trismegistus
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Y'know, if I was in your position,(not having money to order chemicals) I might see wisdom in running around trying to get a job as a stockboy in Janitors supply house.

The pay might suck but.....

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Saerynide
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Money is a big issue, but parents are a even larger issue. They'll freak if they saw something like reagent grade sulphuric acid in the house/garage and they'll wonder why Im buying this sort of stuff.
On the other hand, if I made the substance myself, then I just say "Im learning from it" which is true (and its more fun than just buying the chemical)

 Quote: I might see wisdom in running around trying to get a job as a stockboy in Janitors supply house.

Im a girl btw
Quantum
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I just tried this and got some results. I boiled the salt/water solution and let it cool down a bit. I used mild steel electrodes(I have nothing else) and used about 250ml of saltwater. I have an computer power supply that outputs 5v at 20amps. I got an old CD and drilled 2 holes in it for the electrodes and put them in the holes. The round hole in the middle I covered with some plastic. After about 20min of action the power supply started buzzing. When it does this it seems to mean that there is too much load and I have to unplug it and replug it back in. This also happens if I touch the 2 wires together. I got a nasty brownish solution and one electrode was eaten away. What did I do wrong?

Sadly I had to pour the soultion down the sink because my mom was coming home.

What if, what is isn\'t true?
blazter
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PC power supply

I too have attempted to put an old AT computer power supply to use. My problem now seems to be getting the thing to maintain regulation. When I immerse the electrodes, the voltage drops dramatically to a fraction of a volt and it would appear that the current decreases as well.

In an attempt to load it somewhat I stuck a 60w 120v lightbulb in series with the cell. This seemed to do very little to help and as I suspected it lowered the voltage even more. Now, the interesting part is that by mistake I shorted the leads of the bulb so that it was sort of in parallel. The voltage would drop only very slightly, and more current seemed to be flowing (much more bubbles).

If your power supply is buzzing, then it is probably not very happy for some reason. My guess is that if you run it much longer like that it'll go up in smoke.
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I think you may have discovered the world of "foldback limiting". If you put a low enough resistance load onto a PSU it realises that it cannot hope to maintain the voltage so it gives up trying. This is a useful idea because it stops as much damage being done when thigs go wrong. OTOH it's a pain in the neck if you don't have the "right" load for the PSU.
Have you got a 12 V lamp you can use as a load in series with the cell?
Geomancer
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It might be worth reading the specs of your power supply, if you can find them in a language you understand (cheap PSU might be hard to trace). Many such PSU have minimum currents needed to maintain regulation. For general purpose use you can make an adjustable linear for a few USD. Very useful, though your current capacity could be too small to make large quantities of electrochemicals.
Quantum
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Thanks! I can wire up a light in parallel with the cell. What type of light is best. Some of you say a 60w ad some say a 12volt light. The PSU output is 5volts at 20amps.

Was the brownish colored liquid I got normal or was that from the mild steel electrodes corroding and not NaOH. I expect that the NaOH takes many hours to make and because my PSU started "buzzing" the reaction stoped.

What if, what is isn\'t true?
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 Sciencemadness Discussion Board » Special topics » Technochemistry » NaOH Select A Forum Fundamentals   » Chemistry in General   » Organic Chemistry   » Reagents and Apparatus Acquisition   » Beginnings   » Responsible Practices   » Miscellaneous   » The Wiki Special topics   » Technochemistry   » Energetic Materials   » Biochemistry   » Radiochemistry   » Computational Models and Techniques   » Prepublication Non-chemistry   » Forum Matters   » Legal and Societal Issues