Calling WB + CG -- Redox ??

[Chasville]

WaterBear made this statement in a posting I just read

as an oxidizer it would be chlorine.
the redox potential of chlorine is 1.36 while the redox potential for all forms of oxygen, including ozone are 1.24 or less. The active oxidizer in KMPS is oxygen. The higher the number the more effective the oxidizer. Nothing to do with pound for pound at all. It's an absolute.

I remember reading elsewhere, multiple times, that the Redox "value" for Ozone was 2.0, not 1.24. So, what's the deal?

 

[JasonLion]

Redox potential is measured from one place to another place. Carbon, as it occurs in organic molecules, has a redox potential of approximately -0.42 volt. Oxygen is about +0.82 volt. So Oxygen stealing an electron from organic carbon is 1.24 volts. There are other places oxygen could get electrons from, not typically found in pools, which will give you higher values.

 

[Chasville]

You can't use the same oxidation potential for ozone as for oxygen.

http://www.rsbs.anu.edu.au/O2/O2_1_Redox.htm

O₂ holds together more tightly than the three atoms in O₃.

If Ozone had a weaker oxidation potential than chlorine, then it wouldn't be able to oxidize chloramines, re-releasing the CL^- which it can. At least, that's my understanding/rememberance.

 

[Guest]

You can't use the same oxidation potential for ozone as for oxygen.

I didn't. Read what I wrote again and pay attention to the words "or less".

WaterBear made this statement in a posting I just read

as an oxidizer it would be chlorine.
the redox potential of chlorine is 1.36 while the redox potential for all forms of oxygen, including ozone are 1.24 or less. The active oxidizer in KMPS is oxygen. The higher the number the more effective the oxidizer. Nothing to do with pound for pound at all. It's an absolute.

 

[chem geek]

As I noted in this post, the standard electrode potential of monopersulfate (MPS) is +1.85V while for hypochlorous acid it is +1.611V. For ozone it is +2.076V (see here, for example).

However, this is mostly meaningless unless you are looking at whether a certain redox reaction CAN occur (not that it WILL occur). Just because something has a stronger standard electrode potential does not mean that a specific reaction will occur. It just means that the chemical can potentially react with more substances in redox reactions -- technically it can react with any that have a lower potential (with the lower reaction going right to left). Also remember that these potentials are measured at (or adjusted for) standard concentrations which is 1 mole/liter for solutions (so for reactions with H⁺, that's a pH of 0) and 1 atmosphere for gasses so actual potentials are different under different conditions -- but order-of-magnitude, the ranking is still useful.

Whether a reaction occurs in a timely fashion is a matter of reaction kinetics. The standard electrode potential is related to thermodynamics which says whether a reaction can potentially occur, but it doesn't say how long it will take. The oxygen in the air theoretically (from a thermodynamic point of view) should completely oxidize much of your body's organic compounds to carbon dioxide, but fortunately the reaction kinetics of this are so slow that in practice it doesn't happen at normal temperatures. It does, however, happen at higher temperatures such as when burning wood and this is because one overcomes the activation energy of the reaction -- that is, the reaction rate becomes much faster.

Is there some sort of point to this thread? Ozone is a strong oxidizer and will oxidize some chemicals faster than chlorine, but why does that matter? In a properly chlorinated pool, one rarely needs to shock and the organic buildup is minimal. Ozone might have some more use in a high bather load situation though it can also oxidize some chlorine to chlorate (via chlorite).

Richard

 

[Guest]

Is there some sort of point to this thread? Ozone is a strong oxidizer and will oxidize some chemicals faster than chlorine, but why does that matter? In a properly chlorinated pool, one rarely needs to shock and the organic buildup is minimal. It might have some more use in a high bather load situation though it can also oxidize some chlorine to chlorate (via chlorite).

Richard

I think the point is that the OP is experimenting with ionizers and ozone instead of using chlorine, even though we know that it's an approach that does not work well nor keep the water sanitized.
(as per this in their sig:
"!!! CAUTION !!! Mad/crazy/eccentric scientist/engineer/old_man experimenting with ionizer and ozone -- don't you try it -- Muaha ha ha ha !
Use BBB it makes more $EN$E)")

However, they can do what they want since it is their pool.

 

[Chasville]

The point is that what I had read/found before agrees with the numbers Chem Geek reported, 2.0 for Ozone and for chlorine I had remembered maybe 1.7ish but it could have been 1.6.

So, that being that, why was WB using the numbers he was using? Where did they come from? Why do his numbers indicate that Ozone is a less effective oxidier than chlorine?

To me, the information is conflicting.

Also, as a computer geek of sorts (and data analyst, of sorts), I am acutely aware of sales and marketing mis-use of numbers. I also know I am not infallible in my interpretations of things. I had based some of my justification/decision on the use ozone (and its expense) from the published 2.0 number. Now, if that is the wrong number to use to make a sensible comparison with, then I'd like to know the truth. I'm not the sort that likes walking around naked without knowing.

Also, I don't want to get into a tug of war about my chemistry decisions, so if we can avoid the soap boxes and just discuss the detailed explanations of what's what and the why's, I'd be grateful.

I took some time to peruse through the link CG provided that has a chart of redox potentials for may reactions and many materials. It seems that oxygen and ozone and chlorine "compounds" have many ways to go and various potentials. I see that the "marketers" seem to have glombed onto the most favorable numbers for their purposes, sans science (not too surprising). But, aren't the reactions with the greatest potential the ones most probable to occur? Or are we missing a number? I remember there being a curve, where the current state is at one level, then there is this wall and a slope on the other side. For instance, the thermite reaction between aluminum and iron oxide is incredibly exothermic, but the wall it has to overcome is pretty big. That was why the chemistry teacher used a magnesium "fuse" to set the correct temperature for the mixture to take off with.

 

[chem geek]

So, that being that, why was WB using the numbers he was using? Where did they come from? Why do his numbers indicate that Ozone is a less effective oxidier than chlorine?
:
I had based some of my justification/decision on the use ozone (and its expense) from the published 2.0 number. Now, if that is the wrong number to use to make a sensible comparison with, then I'd like to know the truth.
:
I took some time to peruse through the link CG provided that has a chart of redox potentials for may reactions and many materials. It seems that oxygen and ozone and chlorine "compounds" have many ways to go and various potentials. I see that the "marketers" seem to have glombed onto the most favorable numbers for their purposes, sans science (not too surprising). But, aren't the reactions with the greatest potential the ones most probable to occur? Or are we missing a number? I remember there being a curve, where the current state is at one level, then there is this wall and a slope on the other side. For instance, the thermite reaction between aluminum and iron oxide is incredibly exothermic, but the wall it has to overcome is pretty big. That was why the chemistry teacher used a magnesium "fuse" to set the correct temperature for the mixture to take off with.

If you read the post of mine that I linked to, I explained where waterbear was getting his chlorine number, using chlorine gas instead of hypochlorous acid. The +1.24V comes from the +1.229V for oxygen in the table I linked to (there are small variations in different tables as these numbers get remeasured and slightly improved over time), but it does not apply to ozone which has a higher potential (i.e. waterbear was wrong about that, but keep in mind that he make less mistakes than I do and we correct each other in any event).

You based your justification on a false single number to use. Your description of the "curve" is correct where the difference in potential (height level of the curve) for the reactants vs. the products is the thermodynamic (Gibbs) energy difference which is also related to the difference in electrode potential for redox reactions. It is NOT, however, a predictor of whether the reaction will occur because of the "hill" of activation energy that must be overcome and as you point out higher temperature can get you over that hill. However, the heat of reaction ("exothermic" that you mentioned) is just one component of the thermodynamic energy -- entropy is another factor.

The bottom line is that you should absolutely, positively, not base a purchase decision for ozone on a single redox potential number. Heck, if that were the case, you should just dump some fluorine (F₂) or Praseodymium ion (Pr⁴⁺) or Terbium ion (Tb⁴⁺) or xenon flouride (XeF) in the pool and potentially oxidize even more including the metal in your pool. The fact is that what makes hypochlorous acid so great as a fast killer of bacteria and viruses is that it looks a lot like water (compare HOCl vs. H₂O), is a neutral molecule, and a fairly reactive oxidizer (but also for substitution reactions which are not redox reactions but disturb the normal functioning of proteins and other organic substances).

Chromic acid (H₂CrO₄) with sulfuric acid (aka Jones reagent) is a very strong oxidizer that will oxidize many organic compounds, yet the redox potential of HCrO₄^- is only +1.35V. You simply cannot look at the standard electrode potential to predict actual chemical reactivity. You can only use it to predict when something cannot possibly happen (at least spontaneously without energy input as with electrolysis or photosynthesis).

Since you've got to have some chlorine in the water for disinfection anyway, you might as well look at it for oxidation as well. It's a reasonable oxidizer in most cases, especially for residential outdoor pools. You can, of course, buy more chemicals or equipment to your heart's content, but it is not necessary to do so.

Richard

 

[Chasville]

Ok, so Ozone is a better oxidizer than chlorine = hypochloric acid. But the marketing number, while technically correct from one perspective, is mis-leading in fully understanding its effectiveness.

I understand that the Ozone leaves the water too quickly to be an effective replacement for chlorine in a pool versus sanitizing drinking water. The pool is an open reservoir versus drinking water which is forced through plumbing forcing more complete contact and a higher controlled concentration. In a pool, all the water that is mixed with the ozone in the plumbing is effectively treated, but then it gets dumped into the open reservoir, where the Ozone is unable to reach the full volume. So even though I have a 21,000 gallon pool, and 21,000 gallons is passed through the plumbing and treated in about 8 hours, the water that reenters the pool is effectively recontaminated before it is pumped back through the system, and it is not necessarily true that all of the water passes through the system in 8 hours. Some surface water is not pulled in through the skimmer, and running just the main pump does not necessarily draw all the water down through the main drain, even though the newly cleaned water enters at the top.

Oh, and part of the problem with a pool versus drinking water, is that the source and destination of the water is the same for a pool. Where with drinking water, the source reservoir is not the same as the destination, again forcing/guaranteeing that all the water is effectively treated.

Is it safe to say that I've got this part of the picture correct?

 

[chem geek]

Yes, you've basically got it, at least as far as explaining why ozone should not be used by itself as a sanitizer in pools. It does not remain in the bulk pool water and recontamination occurs far faster than the time for a turnover. Also, it take 4.6 turnovers of the water for 99% of it to get through the filtration and therefore ozonator system, and that's best case. One turnover only has around 63% of the water go through the ozonator -- some water goes through twice, some three times, but 37% doesn't go through at all in the time for one turnover.

Now, that said, having a system that oxidizes compounds in the water during filtration/recirculation isn't bad in high-bather load situations since in that case it can be a useful supplement to chlorine though isn't necessary (i.e. it's an option). That is not generally the case for most residential pools, however.