Sciencemadness Discussion Board

HCl by Electrolysis

Abromination - 25-8-2018 at 17:02

By using electrolysis, I am going to make HClO and attempt to turn it into hydrochloric acid. The procedure is as follows:

In one beaker, I will make a solution of sodium chloride in distilled water. In another, I will add an equal amount of tap water. I will use a strip of filter paper soaked in tap water as a salt bridge. Using graphite electrodes, I will put the anode into the salt water and the cathode into the tap water. I will electrolyse it for a day.
Here comes the part I am unsure of:
I will add a pinch of copper oxide to the hypochlorous acid and it should decompose into hydrochloric acid.
Will this work?

Abromination - 25-8-2018 at 18:54

Well don't everyone answer at once!

IMG_3235.JPG - 1.7MB

WGTR - 25-8-2018 at 19:10

Looking at the setup, I think that you're heading into the right direction, with some possible changes or improvements to the setup.. I can't say much specifically without trying it myself. Otherwise I might be leading you astray. Have you thought of making a glass HCl burner, and just burning the hydrogen and chlorine together as they're made?

Abromination - 25-8-2018 at 20:46

I have considered that, although I can't for safety reasons. It appears to be working.I occasionally add more sodium chloride to the salt cup, the hypochlorous acid beaker is slightly acidic, and the other one is slightly slippery. Not very at all, but its only been a few hours. Do you know if the HClO will decompose to HCl under copper oxide?

UPDATE: I added mor NaCl and it is working really well. The sodium hydroxide feels quite slippery (don't worry I knew it wasn't concentrated yet and I washed it off quickly) and is now highly basic. The hypochlorous acid is at around the right pH but I am going to let it sit overnight.

[Edited on 26-8-18 by Abromination]

fusso - 25-8-2018 at 20:53

Maybe also add some NaOH to anode beaker to neutralize any acidic species and keep them dissolved?

Abromination - 25-8-2018 at 21:14

Quote: Originally posted by fusso  
Maybe also add some NaOH to anode beaker to neutralize any acidic species and keep them dissolved?

I want the acid though. Thats what I am aiming for, although I would if I where to be going for the sodium hydroxide. Im not worried about contamination in the annode beaker (which of course is where the HClO is) because the Na+ is traveling over the bridge.

WGTR - 26-8-2018 at 08:22

Adding chlorine to water produces both hydrochloric and hypochlorous acid. The equilibrium is not strongly to the right as I understand. You can test this theory by adding hydrochloric acid to bleach. In that case, chlorine gas is released from the solution (careful). I think that for this to work efficiently, chlorine would have to be added to the water under pressure.

Chlorine monoxide could be dissolved into water to produce hypochlorous acid directly, but I think that once you start converting some of it to hydrochloric acid, then the previous problem resurfaces, and the solution starts emitting chlorine gas.

If this is just for learning (and not as a practical preparatory exercise), then I would say that I have produced small amounts of hydrochloric acid with electrolysis, using high surface area activated carbon electrodes. The voltage across the cell is only about 0.6V at the most, and the cell charges up much like a capacitor charges. No charges are crossing the double layer boundary at the electrode-solution interface due to the low voltage, and no gases are produced. After several days, the charging current drops close to zero, and each electrode is removed from the solution and rinsed thoroughly. The anode material is infused with chloride, and the cathode material is infused with sodium ion. If you want sodium chloride solution again, you simply stir the cathode and anode material together for a day or two so that the charges recombine. If you want some hydrochloric acid, then you can take the cathode material from some other acid salt that you have electrolyzed (hydrogen ion), and mix that with your chloride electrode material. You should see a pH drop in the solution. Another option is to use the chloride electrode as the cathode, and use a graphite anode (at low current density), and essentially do a reverse electrolysis, where you are combining the chloride with hydrogen at the cathode. In that case I think that the only gas produced should be oxygen, at the anode. If the HCl concentration is dilute enough there shouldn't be any chlorine produced, and the vapor pressure of HCl should be low enough that the oxygen won't strip it from solution. To concentrate the acid to a lesser diluted form, you let it sit out and evaporate down.

[Edited on 8-26-2018 by WGTR]

Abromination - 26-8-2018 at 10:17

Quote: Originally posted by WGTR  
Adding chlorine to water produces both hydrochloric and hypochlorous acid. The equilibrium is not strongly to the right as I understand. You can test this theory by adding hydrochloric acid to bleach. In that case, chlorine gas is released from the solution (careful). I think that for this to work efficiently, chlorine would have to be added to the water under pressure.

Chlorine monoxide could be dissolved into water to produce hypochlorous acid directly, but I think that once you start converting some of it to hydrochloric acid, then the previous problem resurfaces, and the solution starts emitting chlorine gas.

If this is just for learning (and not as a practical preparatory exercise), then I would say that I have produced small amounts of hydrochloric acid with electrolysis, using high surface area activated carbon electrodes. The voltage across the cell is only about 0.6V at the most, and the cell charges up much like a capacitor charges. No charges are crossing the double layer boundary at the electrode-solution interface due to the low voltage, and no gases are produced. After several days, the charging current drops close to zero, and each electrode is removed from the solution and rinsed thoroughly. The anode material is infused with chloride, and the cathode material is infused with sodium ion. If you want sodium chloride solution again, you simply stir the cathode and anode material together for a day or two so that the charges recombine. If you want some hydrochloric acid, then you can take the cathode material from some other acid salt that you have electrolyzed (hydrogen ion), and mix that with your chloride electrode material. You should see a pH drop in the solution. Another option is to use the chloride electrode as the cathode, and use a graphite anode (at low current density), and essentially do a reverse electrolysis, where you are combining the chloride with hydrogen at the cathode. In that case I think that the only gas produced should be oxygen, at the anode. If the HCl concentration is dilute enough there shouldn't be any chlorine produced, and the vapor pressure of HCl should be low enough that the oxygen won't strip it from solution. To concentrate the acid to a lesser diluted form, you let it sit out and evaporate down.

[Edited on 8-26-2018 by WGTR]


Well then, I guess I am going to be finding uses for hypochlorous acid. Copper oxide, I found apon further reasearch, decomposes perchloric acid, not hypochlorous acid. Anyone know what I can do with hypochlorous acid? Also are there other good ways to make HCl without sulfuric acid?

EDIT: I might try the reverse electrolysis. What do I need to know if I do that?

[Edited on 26-8-18 by Abromination]

WGTR - 26-8-2018 at 15:15

Quote: Originally posted by Abromination  

EDIT: I might try the reverse electrolysis. What do I need to know if I do that?[Edited on 26-8-18 by Abromination]


I know you're on a budget, so I don't want to tell you to go out and buy stuff, especially since I can't give you a good bill of materials and plans that are guaranteed to work the first time. However, if you want to learn about the theory behind the idea, you can glance through the Wiki article here about capacitive deionization. You can basically take two small beakers and pack them tightly with activated carbon (like the stuff used in fish tank filters), and electrically connect to them with two graphite electrodes. You can connect the two beakers with a salt bridge like you're already doing. You'd need a power supply that can put out 0.6-1.0 volts, and a current meter would be nice, so you know when the charging current drops, and the cell is fully charged.

Basically, this is an electrical double layer capacitor. You can charge it up and recover the charge as electricity, or disassemble the electrodes and recover the various ions from the electrode structures.

Abromination - 26-8-2018 at 22:10

Quote: Originally posted by WGTR  
Quote: Originally posted by Abromination  

EDIT: I might try the reverse electrolysis. What do I need to know if I do that?[Edited on 26-8-18 by Abromination]


I know you're on a budget, so I don't want to tell you to go out and buy stuff, especially since I can't give you a good bill of materials and plans that are guaranteed to work the first time. However, if you want to learn about the theory behind the idea, you can glance through the Wiki article here about capacitive deionization. You can basically take two small beakers and pack them tightly with activated carbon (like the stuff used in fish tank filters), and electrically connect to them with two graphite electrodes. You can connect the two beakers with a salt bridge like you're already doing. You'd need a power supply that can put out 0.6-1.0 volts, and a current meter would be nice, so you know when the charging current drops, and the cell is fully charged.

Basically, this is an [url=https://www.murata.com/en-us/products/capacitor/edlc/techguide/principle]electrical double layer capacitor
[/url]. You can charge it up and recover the charge as electricity, or disassemble the electrodes and recover the various ions from the electrode structures.


Hah, you are right about the budget. I am saving up for a professional trombone (yes I am also a lover of music and music writing) and am not planning on being able to spare much for chemistry for a long while (a year or two even?)
This is a cool idea however, and may just do it as a progect for school.
I have a very nice multimeter but no real power supply. I just sacrifice batteries to the cause. I could write an interesting paper on this, given the opportunity.