[Sweetmormon]

Ok y'all I'm really new this whole forum thing, so please bear with me. I am a starting amateur chemist, But I LOVE IT. It is really a cool passionate feeling I have to learn about chemistry, especially towards organic chemistry, the power to alter substances as you see fit through your knowledge of thermodynamics, probability, and reactivity. Anyways.. To the point, as this is my first post:

I have a question. I am totally at a loss in understanding what reaction took place in my little electrolysis experiment. I had a big ice cream bucket full of water and salt, I made a copper and graphite electrode which I made from a construction pencil lead. I took 12vdc and used the copper with the positive labeled wire from the power supply, and the graphite with the negatively labeled wire. A gas immediately started to be produced, which I assumed was Hydrogen gas. I have looked a lot of information up on the internet but this particular combination of graphite and copper I could not seem to find.

The copper rod produced no gas but began to get a yellowish/white coating on it and the water began to turn a bluish color, along with a small amount of white precipitate started floating on the surface. No smell of chlorine present. ??I was confused I thought that the copper wire (attached to the negative labeled wire from the power supply) would be negative thus producing the H2 gas and the graphite would be positively charged and start to produce the chlorine gas.

So I switched the wires on each electrode. Then an immediate smell of chlorine filled my nose and I knew it was working like I thought. But I wanted to start a new batch fresh maybe to isolate the NaOH that I would produce.
 

I thought that if I where to separate the two electrodes into two containers connected with a rag already extremely saturated with really concentrated salt water, the one container with the graphite electrode(now with the positively labeled wire attached to it) and salt water in it, and the other with regular water and the copper electrode that the sodium ions might come through the rag to produce sodium hydroxide in the container with the copper electrode in it and the graphite electrode in the other container would start producing chlorine gas..,

..But the graphite didn't produce any gas, but there was a faint smell of chlorine. And the copper wire started producing a gas I presumed to be hydrogen.  I didn't know if it was taking a long time to happen or what.

so I got impatient and put the copper electrode in the same container as the graphite electrode (with the wires now attached oppositely to each electrode from when I started with the ice cream bucket), and the water went really quickly from yellow to blackish with a brownish/blackish precipitate forming. chlorine I think was still being produced as I could see the graphite now visibly producing a gas, and the smell of chlorine was again strong..

What happened in all three different situations???
My goal is to produce Cl2 and harness it to make HCl in another container bubbling it up through water, and to make good NaOH on one side.
???Would it make bleach(sodium hypochlorite) if both electrodes were in the same container (with the same conditions as the third final situation)
Was the blue from Copper Chloride forming in the first situation?
Was the black in the third situation copper solid, or copper oxide? Was NaOH produced in the third situation?


I know this is long winded but I am really confused on how the salt bridge and the inert electrode effected this experiment....
-Thanks for all of your help

[Borek]

Blue in the solution is dissolved copper (oxidized to Cu(II)).

Brown things you see are most likely just a dispersed graphite from the pencil.

You can easily check the identity of the gases produced by collecting them in test tube and using a burning splinter.

I am afraid most of other observations are not easy to explain. My bet is that neither water you used, nor copper, nor graphite are pure - so in fact you have plenty of other elements/compound floating around and making the situation much more complicated than expected.

[Sweetmormon]

Thanks for helping, its pretty confusing

The copper electrode showed no signs of erosion, and the i still dont get whether the blue was copper hydroxide or copper chloride. And what does the salt bridge cause in the case with one solution of brine and one of regular water

[Borek]

Copper cations are blue in water, counter ion doesn't matter.

[Zyklonb]

The copper rod produced no gas but began to get a yellowish/white coating on it and the water began to turn a bluish color, along with a small amount of white precipitate started floating on the surface. No smell of chlorine present. ??I was confused I thought that the copper wire (attached to the negative labeled wire from the power supply) would be negative thus producing the H2 gas and the graphite would be positively charged and start to produce the chlorine gas.

I'm not sure why the reaction wouldn't work this way. I think I've tried this arrangement before and it worked. Most of the chlorine would react with the carbon to produce carbon tetrachloride, but you should still smell some chlorine. The lack of hydrogen produced at the cathode (- electrode) suggests that it simply wasn't conducting electricity, perhaps the connection was bad.

So I switched the wires on each electrode. Then an immediate smell of chlorine filled my nose and I knew it was working like I thought. But I wanted to start a new batch fresh maybe to isolate the NaOH that I would produce.

It should work either way IIRC, I'll have to try that out tomorrow.

I thought that if I where to separate the two electrodes into two containers connected with a rag already extremely saturated with really concentrated salt water, the one container with the graphite electrode(now with the positively labeled wire attached to it) and salt water in it, and the other with regular water and the copper electrode that the sodium ions might come through the rag to produce sodium hydroxide in the container with the copper electrode in it and the graphite electrode in the other container would start producing chlorine gas..,

That is how it should work.

..But the graphite didn't produce any gas, but there was a faint smell of chlorine. And the copper wire started producing a gas I presumed to be hydrogen.  I didn't know if it was taking a long time to happen or what.

The reason the anode didn't produce any (visible) gas is because it reacted (as stated above) to produce carbon tetrachloride, small hints of chlorine did escape. Yes, the cathode produced hydrogen.

so I got impatient and put the copper electrode in the same container as the graphite electrode (with the wires now attached oppositely to each electrode from when I started with the ice cream bucket), and the water went really quickly from yellow to blackish with a brownish/blackish precipitate forming. chlorine I think was still being produced as I could see the graphite now visibly producing a gas, and the smell of chlorine was again strong..

The black is almost certainly copper oxide/hydroxide. Why it formed that rather than soluble chloride is a mystery to me - the only viable possibility I can think of is there were hydroxide anions already in solution.

What happened in all three different situations???
My goal is to produce Cl2 and harness it to make HCl in another container bubbling it up through water, and to make good NaOH on one side.

In the first situation, like I said, there might have been a connection issue. In the second situation, the reaction went as expected, the reason for only a small amount of chlorine is because the current dropped as it went through your salt bridge, so the reaction went slower, and the chlorine was consumed nearly as fast as it was isolated. The last situation went as expected as well, except for the copper hydroxide produced, which is likely due to hydroxide in solution beforehand.

Was the blue from Copper Chloride forming in the first situation?
Was the black in the third situation copper solid, or copper oxide? Was NaOH produced in the third situation?

Yes, the blue is copper ions. Yes, the black is copper hydroxide and possibly oxide. Yes NaOH was produced in all situations (except where current didn't flow).
The blue is not from copper hydroxide, as that is insoluble.

Would it make bleach(sodium hypochlorite) if both electrodes were in the same container (with the same conditions as the third final situation)

Yes, but not entirely. The sodium ions travel to the cathode, where they are reduced to elemental sodium, which of course react with water to produce the hydrogen and sodium hydroxide. The NaOH eventually migrates to the anode and reacts with the chlorine as it's produced, this can either produce NaOCl, or NaClO₃ at lower or higher temperatures respectively.

[billnotgatez]

A link for additional information
https://en.wikipedia.org/wiki/Chloralkali_process

@Zyklonb
Some things you said that surprised me

Most of the chlorine would react with the carbon to produce carbon tetrachloride

The black is almost certainly copper oxide/hydroxide

And this I found interesting

The NaOH eventually migrates to the anode and reacts with the chlorine as it's produced, this can either produce NaOCl, or NaClO3 at lower or higher temperatures respectively.

Do you have a publication that backs up your analysis or is your deductions based on your own experiments?

I personally have some doubts about the reaction intermediates during electrolysis of brine, but have found little that is different from the WIKI posted in this response.

[Zyklonb]

I looked but couldnt find where I read about chlorine and how it reacts with carbon under those conditions. Perhaps I can look more later...
About the copper hydroxide, why is this hard to understand? I use copper as an anode to make copper oxide all the time. I'm just surprised it made hydroxide with chloride ions in solution. It could be carbon particles, or both. There's no way I could be sure as I can't see it.
As for chlorate production and the chloroalkili process, I happen to know a fair deal about such things, I run a big chlorate cell myself.

[Borek]

Off the top of my head...

This was not off top of your head, it was copied from http://www.utahpyro.org/compositions/PreparingChlorates.pdf

Please post links to such documents, for copyright reasons do not copy huge parts of the text here.

[Zyklonb]

Oh, I see, I started typing what I could remember, the realized I could find it elsewhere and paste it. I thought I took out the "off the top of my head" part, but guess not.
Anyway, have copyright lawyers really complained about that sort of thing before?

[Sweetmormon]

Wow everybody i really appreciate all of the help these forums are awesome!! I did try again speratingvthem and have successfully produced the naoh i was searching for! The reaction worked well.
Is the naoh produced in the distilled water (seperated from the salt water by a salt bridge) because na ions flow into solution due to the escape of h2 which produced oh- ions at the electrode? Do th Cl ions stay in the salt bridge or instead flow into the brine to replace the loss of cl in the brine container? tthus equalizibg the na+ ions that left the salt bridge earlier....

And again thanks everyone you guys are awesome

[Borek]

Where the ions go depends on the current flow and electrode reactions. Basically every part of the solution must stay electrically neutral and flow of the current means migrating ions. So yes, if you have hydrogen escaping that means you are removing H⁺ from the solution, and it must be replaced by Na⁺.

Note that if you use distilled water as any part of the solution you will need much higher voltage to maintain the current.

[Zyklonb]

Note that if you use distilled water as any part of the solution you will need much higher voltage to maintain the current.

Not necessarily, even pure water conducts electricity, due to it's self ionization. Of course only a tiny amount, however the pure water will soon be replaced with a sodium hydroxide solution, which conducts electricity easily, so it will take a little while for the reaction to go at a reasonable rate, but it will get going quite fast. 

[Borek]

even pure water conducts electricity, due to it's self ionization

No. Ultra pure water at specific resistance of 18MΩ is a pretty good isolator. So good it is practically impossible to measure its pH with a standard pH electrode.

Typical DI/RO water is not that good, with a specific resistance around 1MΩ. While you are right it will eventually get replaced with a sodium hydroxide solution, adding such a high resistance in the circuit typically means initial current in the μA range. Good luck waiting till it gets into A range.

[Mercuric cyanide]

 You could just put a little sodium hydroxide in the distilled water beforehand.

[Zyklonb]

Ok, even still distilled water generally contains small amounts of carbon dioxide/carbonic acid as well as other miniscule impurities. I always use distilled water, and the reaction speeds up so fast you can see the gas evolution speed up quickly. Other experiments suggest that my PSU goes to full power practically immediately, so slow power increase is out of the question. Either my distilled water is less purer than usual, or the reaction works fine.

You could just put a little sodium hydroxide in the distilled water beforehand.

I should've done that...