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Topic: Salt bridge membrane electrolysis not working  (Read 388 times)

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Offline sprotz

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Salt bridge membrane electrolysis not working
« on: May 16, 2020, 10:42:01 AM »
I am trying to do membrane electrolysis of sodium bicarbonate by using a salt bridge which is a paper towel soaked in electrolyte and one end dipped in bicarbonate solution, the other dipped in plain water. Using carbon electrodes, one in each solution and 12v DC 3A, I switch on the power but nothing happens.
The goal is to form sodium hydroxide, but no electrolysis occurs. I tried to test the system on two containers with salt solution bridged by a membrane. A small amount of bubbling happens.

So I think maybe resistance is too high through the membrane? Or that plain water is just too weak an electrolyte?

Offline Borek

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Re: Salt bridge membrane electrolysis not working
« Reply #1 on: May 16, 2020, 11:43:52 AM »
So I think maybe resistance is too high through the membrane? Or that plain water is just too weak an electrolyte?

Or even both.

What is the current?
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Offline sprotz

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Re: Salt bridge membrane electrolysis not working
« Reply #2 on: May 16, 2020, 01:04:14 PM »
3.25 Amps, 12 Volt power adapter.
But I have noticed the electrolysis picking up after some time. Bubbling is visible and increasing. It seems it needs time for the sodium ions to travel across to the other cell. Adding a little hydroxide to the pure water cell will speed things up.
« Last Edit: May 16, 2020, 01:40:31 PM by sprotz »

Offline Borek

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Re: Salt bridge membrane electrolysis not working
« Reply #3 on: May 16, 2020, 03:09:39 PM »
3.25 Amps, 12 Volt power adapter.

Is that measured current, or the rating of the DC unit you are using?
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Offline sprotz

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Re: Salt bridge membrane electrolysis not working
« Reply #4 on: May 17, 2020, 03:15:55 AM »
That is the rating on the power adapter.

Offline Borek

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Re: Salt bridge membrane electrolysis not working
« Reply #5 on: May 17, 2020, 04:09:29 AM »
That is the rating on the power adapter.

That means it is capable of delivering 3A without burning, not that it always delivers 3A. You need an ammeter in the circuit to measure the current. And knowing the current you will be able to analyse what is going on.
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