Sciencemadness Discussion Board

How to check pH while chorate electrolysis is running ?

metalresearcher - 10-1-2025 at 02:27

When running is session (started with 'diet salt' : 2 parts KCl and 1 part NaCl) there is still a minute amount of Cl2 released because of hypochorite formation, which makes ClO3- due to the temperature of 70 C.
I have added a tiny amount of K2Cr2O7 which makes the liquid a pee yellow color.
I want to check the pH, but the pH papers are bleached because of the even tiny amounts of chlorine.

How can I check the pH ?

khlor - 10-1-2025 at 08:06

try taking a small sample allow it to sit for a while and/or react it the -ClO with MnO2

Edit:text corrections

keep in mind NaClO is slightly basic, if you choose to react it with MnO2 it might throw off the pH results, I think it is not just the chlorine that is bleaching the pH strips. I mean this solution has four oxidizers: chlorine, dichromate, hypochlorite and chlorate, all of which can cause bleaching if I am not mistaken, though, allowing it to sit will remove chlorine gas over time.

[Edited on 10-1-2025 by khlor]

metalresearcher - 10-1-2025 at 09:12

@khlor: So it means that pH cannot be gauged when in a solution of bleach (which it actually is) ?

khlor - 10-1-2025 at 12:52

Quote: Originally posted by metalresearcher  
@khlor: So it means that pH cannot be gauged when in a solution of bleach (which it actually is) ?


I guess, depending on the quality of the strips being used, though I did it with no issue, perhaps his problem is the dissolved chlorine or the strips, or even concentration being too high, thruth be told it was a suggestion based on my experiences with electrolysis, but I mainly did with divided cells, and still, on anode chamber the strips got bleached, but a few minutes after the test, by then I had an idea of the solution's pH. chlorine and free radicals on an elctrolysis cell are harsh to many things, I had epoxy glue reduced to a brittle useless piece of plastic.

Edit: how would you go about it?

[Edited on 10-1-2025 by khlor]

Edit2 : nevermind the question, I didn't see who asked + text corrections

Plus, remeber this is a highly oxidizing solution, it will bleach stuff. you could dilute the solution and do the math, or titration. I never did chlorate cell stuff, but there must be a way to measure the pH

[Edited on 10-1-2025 by khlor]

khlor - 10-1-2025 at 13:16
Quote:

If you want you can control the pH of your cell. This will dramatically increase current efficiency and also give much much less erosion if you are using Graphite anodes. It will decrease erosion on all Anode typed IMO. There is little point in throwing in a 'slash' of acid (say) twice a day in a effort to control pH. You will have to set up a system to drop dilute HCl into the cell. I have heard that 1% solutions are used in industry, but you could probably use stronger. pH stats are used by industry. A pH probe that is permanently immersed in the cell and that is capable of withstanding cell condition will have a high cost.< The best strategy for the amateur is to simpy drop/pump HCl into the cell at a rate that will hold pH in the wanted region. The pH is checked periodicaly using an standard pH meter.

look here

http://www.chlorates.exrockets.com/reaction.html

in the "Controlling pH section, it states that in the industry they use a pH probe and a "standard pH meter" I think they mean the lab pH meters.

drakedevel - 10-1-2025 at 13:19

An electronic pH meter won't have any trouble measuring the pH of a bleach solution. In my experience, even very cheap ones give acceptable results when calibrated and properly maintained.

Dilution is tricky to correct if there are buffering effects in your solution; I don't know enough to be able to gauge whether that's a factor here.

phlogiston - 11-1-2025 at 05:45

If all you have is pH paper, you could take a sample and boil it briefly to destroy the hypochlorite before using the pH paper.

khlor - 11-1-2025 at 08:31

Quote: Originally posted by phlogiston  
If all you have is pH paper, you could take a sample and boil it briefly to destroy the hypochlorite before using the pH paper.


but wouldn't it alter the end result? as NaClO is basic, by destroying it you will end up with NaCl in the solution thus resulting in altered pH plus if the solution is meant to contain HCl, it will also change pH for part of the HCl will evaporate.

Rainwater - 11-1-2025 at 10:55

I have used a standard solution of HCl and Methylene blue indicator to titrate a high ph cell. But when te ph is slightly acidic, the papers strips work well and bleach a few minutes later
Allowing me to read them