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Topic: Saltwater Electrolysis - Adding Hydrochloric Acid  (Read 5478 times)

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Offline HelloCthulhu

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Saltwater Electrolysis - Adding Hydrochloric Acid
« on: August 21, 2012, 02:14:58 PM »
Greetings forum!

I'm experimenting with saltwater electrolysis and have a few questions. I'm using a salt solution I've prepared overnight. The solution has about 2 parts water, 6 parts salt, so I will essentially be electrolyzing brine at the beginning of the experiment (For safety, the experiment is done outside with a fume hood.). At this point, the solution is very dry and flaky, with a voltage of about 1V without current. I'll be using a current of about 1A with a voltage peaking around 5V. The overall reaction should be:

2 NaCl(aq) + 2 H2O(l) → 2 NaOH(aq) + H2(g) + Cl2(g)

However, I will be adding another prepared solution of HCl + H2O to my original solution. How will adding the protonated water to the brine during electrolysis change the reactions? Thank you for your assistance!  :)


Offline Arkcon

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Re: Saltwater Electrolysis - Adding Hydrochloric Acid
« Reply #1 on: August 21, 2012, 03:08:01 PM »
First of all, I wanna say, you're fortunate to be the owner of one of those fancy, outdoor, fume hoods.  So good job there.  You'll have to realize, in less you have some sort of semipermeable diaphragm separating your tow half cells, that the Cl2 will dissolve partially in the water, and react with the NaOH, forming sodium hypochlorite (common household bleach.)  Lowering the pH will re-release the chlorine from the bleach, for a while, at least.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline HelloCthulhu

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Re: Saltwater Electrolysis - Adding Hydrochloric Acid
« Reply #2 on: August 21, 2012, 06:25:26 PM »
"First of all, I wanna say, you're fortunate to be the owner of one of those fancy, outdoor, fume hoods.  So good job there."

I'm using it for the same reason people who paint cars, boats, and planes wear masks outdoors. But then again, they aren't hunched over their work adjusting multimeters, potentiometers, etc. So I went with a fume hood. Plus, I live in Florida. Not very breezy this time of year.

I'm not trying to produce pure gases at the electrodes, but I may consider using a membrane between the A and C sides of the cell in the future. Again, the HCl + H2O solution is already prepared in a separate container that I'll be pouring in during electrolysis of the brine. How will this change the reactions? Will it be 2NaCl + 2H3O now? Any help is greatly appreciated.



 

Offline Hunter2

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Re: Saltwater Electrolysis - Adding Hydrochloric Acid
« Reply #3 on: August 22, 2012, 04:38:29 AM »
Adding of HCl will only neutralize your NaOH and form again NaCl.  It make no sense to add it.

The electrolysis products are the same. On Cathode you will get hydrogen and on Anode Chlorine.

Offline HelloCthulhu

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Re: Saltwater Electrolysis - Adding Hydrochloric Acid
« Reply #4 on: August 22, 2012, 04:23:41 PM »
Thanks for the response Hunter2!

I'm more interested in the behavior of the hydronium ion. I know that before I add the HCl the reactions will be:

2 NaCl(aq) + 2 H2O(l) → 2 NaOH(aq) + H2(g) + Cl2(g)

What about after? Will it be 2NaCl + 2H3O now? Its really important that I learn the reactions. I greatly appreciate the feedback.

Offline vmelkon

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Re: Saltwater Electrolysis - Adding Hydrochloric Acid
« Reply #5 on: September 04, 2012, 03:26:17 PM »
If you add hydrochloric acid to a solution of NaCl, there won't be a reaction between them. All you'll have are ions of Na+, Cl-, H3O+ and higher species of the hydronium ion floating around.

As it was mentioned before, NaOH will form (in solution) during electrolysis. That means OH- ions will be in your solution. Adding an acid would combine the H+ and OH- ions making H2O.
NaOH + HCl -> NaCl + H2O

Another reaction will be between the hyprochlorite ion (ClO-) and you H+ ions.
1 NaClO + 2 HCl -> NaCl + Cl2 + H2O

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