Sciencemadness Discussion Board - Is NaOH from NaCl electrolysis of good quality?

Is NaOH from NaCl electrolysis of good quality?

shaheerniazi - 25-11-2013 at 23:43

When I did electrolysis of NaCl with copper electrodes I got copper(II)hydroxide and Sodium Hydroxide Solution, but my solution doesnt seem good because it doesnt react with aluminum?

[Edited on 26-11-2013 by shaheerniazi]

confused - 26-11-2013 at 05:13

its probably too dilute, did you titrate it to find out it's concentration or molarity?

shaheerniazi - 26-11-2013 at 05:25

Nope, But I think Ill evaporate some water and concentrate it maybe it makes it reactive?

confused - 26-11-2013 at 05:41

concentrating it would work, just be sure to use a reaction vessel that won't react with the NaOH

Metacelsus - 26-11-2013 at 06:03

What kind of cell did you use? It's possible you made sodium chlorate instead of sodium hydroxide. Generally, sodium hydroxide requires a diaphragm.

Pulverulescent - 26-11-2013 at 06:33

Quote:

When I did electrolysis of NaCl with copper electrodes I got copper(II)hydroxide and Sodium Hydroxide Solution

Where do you think the Cl₂ went?
In any case, NaOH cannot be prepared in usable quantities by electrolysis in the way described!

Chloralkali process.

shaheerniazi - 26-11-2013 at 06:37

I used 9 volt battery and the chlorine was reacting with the copper wire to make copper chloride which was stuck on the wire, maybe I made sodium chlorate because when I evaporated it it smelled like clay and when I tried to melt the powder it didnt melt?

MrHomeScientist - 26-11-2013 at 06:53

You need to be more descriptive of your experiments. How was the electrolysis set up? Did you just throw a battery into salt water, or something more sophisticated? What were your anode and cathode materials? Did you use a diaphragm?

If, as I suspect, you just put some wires in a cup of salt water, then you produced (a small amount of) sodium chlorate, not hydroxide. You need separation of the electrodes with a diaphragm for NaOH production - I've found that a common clay flower pot works for this purpose. In my experiment, I used a plastic bucket with a flower pot nested inside it with salt water solution filling both (but not completely submerging the flower pot!). I used a carbon anode and steel cathode, with the cathode in the flower pot. After allowing several minutes for the clay to soak up solution and become conductive, weak NaOH solution is produced in the pot. After the fact, I learned that you don't need (or want) salt water in the cathode compartment. You do need a small amount of ions to make it conductive, preferably a "seed" amount of NaOH.

If you did make chlorate, it would melt at a (relatively) low temperature and decompose into oxygen gas and NaCl. That's what happens with potassium chlorate, anyway. Did you make any attempt to separate your electrolysis product from all the unreacted salt?

[Edited on 11-26-2013 by MrHomeScientist]

shaheerniazi - 26-11-2013 at 07:23

Yes I filtered out the copper(II)hydroxide and stored it in a vial and store the sodium chlorate solution in a bottle.
Though is your method with the flower pot like this?

Pulverulescent - 26-11-2013 at 08:20

'Sorry shaheerniazi, I thought you were describing an open cell . . .
If the pot will allow passage of ions without it being porous enough to permit water circulation it should work, albeit with very low efficiency!

Needs patience . . .

MrHomeScientist - 26-11-2013 at 08:35

Yep that's exactly how I did it, except I had the wires switched. That way, the NaOH is produced inside the flower pot and you can just lift that out. That's really just a preference, though. Either way will work fine; switching the electrodes just changes where the hydroxide and chlorine are made. An improvement would be to put a lid on the flower pot, to prevent chlorine from getting in and reacting with your hydroxide solution. Make sure there's a small hole to allow hydrogen to escape.

The anode should be an inert material like carbon, otherwise it quickly corrodes in the oxidizing environment of chlorine. The cathode material is less important, but graphite is usually a good choice for both.

In my experiment the pot seemed to work great. The only problem of course is the hole in the bottom of those types of containers. I tried sealing it with duct tape and caulk. Tape lost integrity pretty quickly, and caulk lasted a few days before starting to fall apart. I have a data table someplace with NaOH concentration vs. electrolysis time; I'll look for it and post what I have. If I remember right, I ran it for almost a week and it was still quite dilute. That of course will depend on the amount of current you are pushing through the cell.

Disclaimer: no matter how much I read about it, I am notorious for confusing what anode and cathode mean. As I write this, I believe the anode is the positive wire and the cathode is the negative wire. That perception could change at any minute. Someone please correct me if I've made any mistakes.

[Edited on 11-26-2013 by MrHomeScientist]

shaheerniazi - 26-11-2013 at 08:41

Exactly I always get confused at where is the anode and cathode, even while making the image I got confused so I did not label the electrodes.

Pulverulescent - 26-11-2013 at 09:42

Cl^- gives up its electron at the anode ─ Na⁺ collects an electron at the cathode.

Hope that helps . . . ?

JJuan - 2-2-2015 at 18:08

Hi guys, i am trying too to obtain Na(Oh) through NaCl's electrolysis in solution. But i cant avoid the formation of NaClO, how can i do a diaphragm or a membrane? Is there any material easy to get that works as Na+ exchange? another thing that i was thinking is that if let the electrolysis continue for several hours and according this:

Electrolysis of Sodium Hypochlorite solution

``You will get all kinds of rather complex reactions at the anode, which lead to formation of chlorate ion, chloride and oxygen. At the cathode you will get some hydrogen, but almost certainly there will also be reduction of hypochlorite to chloride ion:

ClO(-) + H2O + 2e --> Cl(-) + 2OH(-)

In fact, this latter reaction may even be the dominant reaction. It is a great problem in electrolytic production of chlorate salts from chlorides. The addition of a small quantity of hexavalent chromium to the solution largely prevents the occurrence of this reaction and then indeed hydrogen gas and hydroxide ions are produced at the cathode. ´´

Could a big part of the Cl2 go away and finally obtain an appreciable amount Na ( OH ) in the solution?

I'm using graphite electrodes and a voltage of 12V.

[Edited on 02-02-2015 by JJuan]

MrHomeScientist - 5-2-2015 at 12:13

I recommend rereading the thread - the flower pot method I use works as a diaphragm, and you couldn't get much cheaper or easier. It's probably not terribly efficient, though, and it would help to isolate the hydroxide chamber from the chlorine fumes produced at the other end. Also it's NaOH, no parentheses needed.

JJuan - 21-2-2015 at 21:27

Thank you for answer, and you are right, I should have to translate all posts. I left trying the electrolysis due to the low efficiency of it, with the resources at my disposal. Actually, my problem is that i'm from Argentina lol, here the sale of NaOH is restricted, so because of that i'm trying to obtain NaOH in apreciable amounts to use it in others experiments. I saw in another thread a method more promising using Na2S which basically involves removing S2- by precipitation. If i get good results with pleasure I share It. I have one idea in mind so if you want to help me you are welcome ha. I want to use a copper anode to corrode and precipitate the highly insoluble CuS, using a graphite or stainless steel cathode at low voltage. What do you think?

kt5000 - 6-7-2015 at 16:00

I've been tinkering with this process as well. With the flowerpot design shown above, is it possible to use a copper anode to produce copper(ii) chloride solution in that cell? Or will there be other products?

[Edited on 7-7-2015 by kt5000]

annaandherdad - 7-7-2015 at 08:53

Quote: Originally posted by MrHomeScientist

I recommend rereading the thread - the flower pot method I use works as a diaphragm, and you couldn't get much cheaper or easier. It's probably not terribly efficient, though, and it would help to isolate the hydroxide chamber from the chlorine fumes produced at the other end. Also it's NaOH, no parentheses needed.

Hi, Mrhomescientist, I know you're interested in demos for kids. I did one with the electrolysis of salt water that was fun. I used a U-shaped glass tube, with corks in the tops with carbon rods penetrating them for the electrodes, and a bit of cotton at the bottom of the U for a crude diaphragm. It doesn't need anything more sophisticated for this demo. I made sure the salt was pure and I used distilled water, since our tap water here is noticeably alkaline. The I put a drop of phenolphthalein in the side with the negative electrode. Now when you turn on the current, the NaOH made at the negative electrode flows down from it, creating beautiful pink sworls that really impress the kids. I also explain to them what's going on.

If you don't have the cotton barrier, then before long the chlorine from the positive electrode comes over and bleaches (ie destroys) the phenolphthalein, and the color along with it.

This is the usual industrial production of NaOH, right? I've wondered how they separate the NaOH from the residual NaCl, but maybe they do what you mentioned, put some seed NaOH in the center cell and then that builds up.

This means the Na+ ions pass through the diaphragm. But why do the OH- ions not do the same? Do you know?

kt5000 - 7-7-2015 at 11:28

Quote: Originally posted by annaandherdad

Any other SF Bay chemists?

I'm in Central California and finishing an A.S in Chemistry this year

A far cry from what the guys here would call "chemist", but it's a start. I'm having a heck of a time figuring out how I'll complete a B.S. while working.

MrHomeScientist - 7-7-2015 at 12:16

annaandherdad,

Thanks, that does sound like a neat demo. I'll have to try it out sometime for the older crowd.

Yes, that's the Chloralkali process used in industry. They use much fancier ion-exchange resins for membranes rather than flower pots, of course

The wiki on that process has a nice graphic that illustrates it, which I can't get to display here despite using the "Insert an Image" button. Basically brine flows into the anode compartment and water (presumably with some ions to make it conductive) flows into the cathode compartment.

I'll admit I don't know why flower pots work as ion exchangers. As for how it works in general, I did find a very nice document "for dummies" that describes it. They aren't kidding about the "for dummies" part either; the first 2 lines say "Water is a liquid. Water is made of water molecules." I promise it gets better after that though (start at page 3).

Basically there are 'fixed' ions and 'mobile' ions. If the fixed ions are negatively charged, they repel negative ions in the solution and allow the positive ones to pass.

Attachment: Ion-Exchange-for-Dummies-RH.pdf (782kB)
This file has been downloaded 562 times

annaandherdad - 7-7-2015 at 16:33

Quote: Originally posted by MrHomeScientist

I'll admit I don't know why flower pots work as ion exchangers. As for how it works in general, I did find a very nice document "for dummies" that describes it.

Thanks, I read the pdf and several wikipedia articles, which clarify things. The wikipedia article mentions that clay can serve as an ion exchanger, which may explain why the flower pot works. But I guess it means that you can only use clay to pass positive ions (what you need in this case). It doesn't elaborate on this property of clay. And I also found (probably) the diagrams you were looking at. There is indeed only NaOH on one side (no NaCl), which answers my question about purification.

kt5000 - 9-7-2015 at 20:53

I ran the flowerpot method tonight, just for kicks. I found the ceramic cup at a local pottery store that sells raw pottery for people to paint and kiln.

That's a 500 mL beaker. There's a saturated NaCl solution inside the ceramic cup with a positive graphite electrode (pencil lead). The solution on the outside is mostly distilled water with a bit of NaOH for electrolyte and a copper negative electrode. They called the cup material 'bisque' and it conducts great.

[Edited on 10-7-2015 by kt5000]