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Topic: Can't seem to make sodium hypochlorite  (Read 524 times)

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Offline sprotz

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Can't seem to make sodium hypochlorite
« on: May 12, 2020, 04:16:25 AM »
I am trying to make sodium hypochlorite by electrolysis using a 12v 1.5 A power adapter with salt solution and carbon electrodes, in a sealed container but for a tiny hole to allow release gas pressure from any gases evolved.  As I understand the solution is supposed to turn greenish yellow, but I don't see any yellow. I continued electrolysis for 5 more hours, still no colour change, only black carbon like particles settling at the bottom, but it does smell like chlorine water. So I left electrolysis to continue overnight, and still no yellow. Instead the whole solution is black-ish. The black is maybe from the rubber used as a plug in the container that is corroded by the chlorine. What am I doing wrong ?

Offline AWK

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Re: Can't seem to make sodium hypochlorite
« Reply #1 on: May 12, 2020, 04:29:56 AM »
How do you detect the presence of hypochlorite in the solution?
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Offline billnotgatez

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Re: Can't seem to make sodium hypochlorite
« Reply #2 on: May 12, 2020, 10:17:58 AM »
What are you using for electrodes?

Are you doing this in a lab or at home?

Offline sprotz

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Re: Can't seem to make sodium hypochlorite
« Reply #3 on: May 12, 2020, 04:49:27 PM »
I am doing this at home. I have since re-designed the electrolysis cell that separates chlorine from hydrogen as it bubbles. It seems chlorine reacted with hydrogen in the previous cell to form hydrogen chloride, but still in this new cell, 2 hours and still no yellow colour. maybe more time?

Offline AWK

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Re: Can't seem to make sodium hypochlorite
« Reply #4 on: May 12, 2020, 05:19:04 PM »
If you want to get hypochlorite, you also need to be able to check it out. How do you know you haven't received it? Hypochlorite is not a yellow-green gas but a colorless substance that is well soluble in water. In addition, you need to know other electrolysis conditions - mixing solutions from the electrode compartments, low temperature, and proper voltage so that water electrolysis occurs as little as possible. Furthermore, the evolving gases sweep the graphite electrodes and hence the gray color of the solution after prolonged electrolysis.
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Offline sprotz

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Re: Can't seem to make sodium hypochlorite
« Reply #5 on: May 13, 2020, 01:56:16 AM »
Then how come every answer on the internet, and every image says that sodium hypochlorite is greenish yellow in solution?  As my electrolysis is going on, I can see white fumes just below the water surface where hydrogen is bubbling. Is the hydrogen reacting with the hypochlorite?

Offline AWK

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Re: Can't seem to make sodium hypochlorite
« Reply #6 on: May 13, 2020, 02:24:02 AM »
In my first post, I advised chemical checking for the presence of hypochlorite in solution.
This may allow you to search for the right electrolysis conditions. The synthesis of sodium hypochlorite by NaCl electrolysis in the way you presented does not make much sense. Hypochlorite is so unstable that you can only chemically confirm its presence. It is obtained by chlorine treatment on a NaOH solution and stabilized by constantly maintaining a fairly basic pH. And for more concentrated solutions, you can see the bright yellow color of the solution that comes from the slowly liberating chlorine formed as a result of decomposition. In very dilute solutions contaminated with crumbled graphite, this color of solution cannot be seen.
You've chosen an electrolytic experiment that's very difficult to carry out, and you don't quite understand its basics.
« Last Edit: May 13, 2020, 02:36:21 AM by AWK »
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Offline sprotz

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Re: Can't seem to make sodium hypochlorite
« Reply #7 on: May 13, 2020, 03:13:47 AM »
I understand the process, electrolysis generates sodium hydroxide and gives off chlorine, which then goes back to dissolve in the newly formed NAOH, I made the setup so as not to allow chlorine to escape, to let it dissolve back and let hydrogen freely escape into the atmosphere , I am aiming for 5% concentration. Does this concentration have a noticeable colour?
I don't know how to test for hypochlorite and the internet search mentions complicated chemicals and kits which I don't have access to.

Offline AWK

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Re: Can't seem to make sodium hypochlorite
« Reply #8 on: May 13, 2020, 03:23:12 AM »
Have you heard of iodide-starch papers? You can make them at home if you have a little potassium iodide (and potato starch). Papers can be stored for months but in the dark.
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Offline sprotz

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Re: Can't seem to make sodium hypochlorite
« Reply #9 on: May 13, 2020, 04:07:53 AM »
Ok, I've seen that 5% can be colourless. I will get the the test chemicals next time but now I am testing it by adding drops of hypochlorite to a liquid containing denatonium benzoate to remove bitter taste. It seems to be working.

Offline AWK

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Re: Can't seem to make sodium hypochlorite
« Reply #10 on: May 13, 2020, 04:14:46 AM »
You have never obtained a 5% hypochlorite solution, only trace concentrations. In addition to chemical degradation, hypochlorite also electrochemically degrades.
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