Pondering SWG's and other things

[Joelin]

OK i have a 2 fold question?
A. Since a SWG breaks down salt to produce chlorine, Does it not by default break down the water (h2o) into hydrogen and oxygen gas ? And if so do the Molecules re-combine to create h2o again or do they simply discharge into the air.

B. What is the purpose of using titanium for the plates. Could you not use copper or brass or other metal than steel because we all know what salt water will do to steel?

Just wondering
Thanks

 

[pooldv]

Sorta, here is what happens,

The whole process is exactly balanced by equivalents: the amount of chlorine produced is directly related to the amount of hydrochloric acid used, other things remaining equal . This could be represented roughly as follows (with the ions all separated in solution):-

2 NaCl + 2 H2O ---------- electrolysis ---------> 2 NaOH + H2 + Cl22
NaOH + 2 HCl ---------chemical reaction--------> 2 NaCl + 2 H2O
Net reaction*: 2 HCl ---------------------------------> H2 + Cl2 (as gases bubbling off)

The titanium plates are coated with ruthenium or iridium.

 

[Divin Dave]

Im not much of a chemist like pooldv,

But yeah, the water turns back into water and the salt turns back into salt. Thats why using a SWG, you do not have to constantly replenish the salt or the water just because your are using SWG.

 

[JoyfulNoise]

Titanium is an important material to use as an electrode base (coated with ruthenium, iridium and other transition metals) because titanium is difficult to electrochemically etch. If the coating wears off in a small patch on the electrode surface, the titanium will passivate and form an adherent oxide coating. This is also how you can get different colors of anodized titanium - you form an adherent oxide on the surface with microscopic pores and varying thickness as you electrochemical anodize it. The thickness of the coating will determine the color of the anodized film.

If you were to use a cheaper base material such as copper or stainless steel (and I think some of the cheaper SWG manufacturers do this), then you will get metal contamination in your water as both copper and steel can and will be etched by electrolysis in water. You can do a simple experiment with a 9V battery, copper wires and some salt water. Place the stripped ends of the copper wires in a cup of salt water and hook them up to a 9V battery. As the current flows through the salt water solution from one wire to the other, one of the wires will disintegrate and release Cu ions (as cupric chloride) into solution and the water will start to turn blue.

 

[pooldv]

Now who is the chemist???

 

[JoyfulNoise]

Now who is the chemist???

Materials Science & Engineering, actually....

Too many years locked away in a metals plating lab pondering all of the electrolysis going on around me (probably explains my affinity for SWG's) ! When you have to bring up a 150gal plating tank that utilizes carboy's full of sulfuric acid and various other "fun" chemicals to play with, you get a whole new appreciation for the letters PPE (personal protective equipment for those not in the world of chemistry).

 

[chem geek]

The detailed reactions are listed under "Salt (SWG) Pool" in this post and is not quite what was shown in the post earlier in this thread.

At the anode, chloride ions are converted to chlorine gas. If there was not a sufficient concentration of such chloride ions then water would be converted to oxygen gas and hydrogen ions. This is why you add enough salt to the pool not only to provide sufficient conductivity but also to have chlorine form instead of oxygen gas. The specialized coatings on the titanium plates also lower the activation energy (overvoltage) to favor production of chlorine over oxygen. The chlorine gas dissolves in water to produce hypochlorous acid and hydrochloric acid.

At the cathode, hydrogen ions are converted to hydrogen gas or equivalently water is converted into hydrogen gas and hydroxyl ions.

The net result of the electrolysis is that water plus chloride ion are converted to hypochlorite ion plus hydrogen gas. So the SWG is essentially making bleach out of water and chloride salt.

As for what happens when the chlorine is used/consumed, it reverts back to chloride salt. Depending on what it reacts with there can be nitrogen or oxygen gases produced.

 

[Joelin]

Ok I understand I Think? But am I right in assuming that the hydrogen gas bubbles just end up floating to the top and get released into the air? Not that it really matters at all. I just remembered 8th grade science class when we broke down water into Hydrogen / oxygen gas using pretty much the same process and was just wondering.

Now, I don't understand the relationship mentioned earlier about it depending on how much hydrochloric acid i use?

I use hydrochloric acid or muratic acid to keep my PH in check, I didn't think that it was related to how much chlorine gas is generated by the SWG? I thought that was determined by the salinity in the water.
Not that it matters really, Just pondering " i already said that"

 

[JoyfulNoise]

Hydrogen gas has low solubility in water so you may see bubbles at the returns, totally normal.

As for acid use, the SWG creates a lot of aeration inside the cell. That aeration causes the outgassing of CO2 which raises the pH of your water. Therefore your acid demand will increase from that.


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[Joelin]

That is certainly true. I have to lower it just about every other week or so.
But nobody has yet to answer the question about what happens to the bubbles?

 

[JoyfulNoise]

That is certainly true. I have to lower it just about every other week or so.
But nobody has yet to answer the question about what happens to the bubbles?

The hydrogen gas bubbles outgas from the pool water surface and the chlorine gas dissolves and forms hypochlorous acid. If the pipe connecting the SWG cell to the pool is a short run, it is possible to get chlorine gas bubbles at the returns.


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