The Chemistry behind pH increase on Salt water Pools

[Yavuz Yavuzer]

I took this issue with numerous manufacturers and received answers that didn't satisfy me.

My personal theory is that the gassing off of H2 molecules cause this.

Any other ideas?

Yavuz Yavuzer.

[Kevin Tucker]

Comments from Tom Lachocki at NSPF- “Hydrogen gas (H2) is pretty strongly bound. When it is formed slowly in a chlorine generator, the hydrogen dissolves in the water and then gases off when it enters the pool. The concentration is so low it is of no consequence. However, if the generator is on and the flow is not, then the gas can form and displace some of the water.”

[Kevin Tucker]

The basic chemistry is there- I hope that we can get some additional comments- I have referred the question to some people outside the industry- but the issue that I am not convinced about- is the formation of h2 as a gas. I agree that if the electrolytic cells(+ & -)  were separate and the gasses contained- then the hydrogen gas would be formed- however in this situation- as long as the water is flowing past a cell with alternating current- I'm not convinced that the hydrogen ions won't stay separate as ions.

If the water flow stops- then there can be problems. I have seen incidences of exploding cells from trapped gasses- but that is for charged electrolytic cells with NO water flow. In that case- I don't think that a vertical chamber is necessarily safer- it might have a slight edge- depending on the residual fluid and how the gasses are trapped.

I hope that another contributor can add some research-

[Yavuz Yavuzer]

I thought  some more about this;

My theory is valid, i think.

The formula for electrolysis of salt should be;

NaCl+2(H2O)=NaCl+2(HOH) = NaCl+HOH+HOH= NaOH(Sodium Hydroxyde)+ HOCl(Hypochlorus Acid)+ H2(remaining Hydrogen).

The H2 will not stabilize in gas form, nor will it ionize so easily. The only thing it will do is gas off.

 

Perhaps this is the reason why Australian and South African Salt generator systems use vertical cells to prevent gas trap shut off in their systems.

Again, this is my theory, I would love to see opposing arguments.

Yavuz.

 

[Kevin Tucker]

Interesting question. I'm not enough of a chemist to answer very definitively- my understanding is this-

I have never heard of H2 molecules forming or gassing off. My understanding is that the ionized Hydrogen doesn't form H2 while in the water- and it won't leave on its own. now electrolysis can do that- but the gasses have to be separated at the electrodes.

My interpretation of the rise in pH is due to the remaining sodium hydroxide left behind as hypochlorous acid is formed. The hypochlorous acid is "used up" killing stuff and oxidizing nitrogen compounds. The resulting ions  lose "energy" as they go through the cycle. Consequently the Hypochlorous acid that was formed when the sodium chloride was "generated" no longer balances the hi pH properties of the sodium hydroxide that is the other part of the reaction.

In addition, many other things do gas off- many combined chlorine compounds- chloramines do gas off- and they do contain Hydrogen ions.

The bottom line of my lay interpretation is that the acids are used up as acids oxidizing stuff- leaving the high pH alkaline materials behind.

 

I hope that we will have a better answer- I have sent a few requests to more knowledgeable people...