Test if it is possible to explain the know ORP reduction when adding H2O2 into a saltwater

[Dan_P]

In my world - free radicals oxidize things and the compounds you mentioned is known to be very strong oxidizer - that make me think that they are "stronger" active radicals (or create more of this sort) than H2O2, May @Randy Holmes-Farley tell us if I´m in the right world or not because I do not know for sure.

Sincerely Lasse

Sometimes reaction rate and free energy difference get mixed up (see table). H2O2 is the strongest oxidizer we discussed but does not act like it according to the ORP. Hydrogen peroxide is acting differently with the ORP probe than chlorine and permanganate. We just have not done the experiment yet to describe how it is acting differently.

 

[Randy Holmes-Farley]

Sometimes reaction rate and free energy difference get mixed up (see table). H2O2 is the strongest oxidizer we discussed but does not act like it according to the ORP. Hydrogen peroxide is acting differently with the ORP probe than chlorine and permanganate. We just have not done the experiment yet to describe how it is acting differently.

I still think it is all well explained by trace element effects, some getting oxidized and some reduced by H2O2, and its mostly the redox active trace elements that are what is actually measured by an ORP electrode.

Lots of highly oxidizing and reducing species have little to no impact on ORP because they do not interact well with the electrode. O2 is a perfect example. H2O2 may be another.

 

[taricha]

@Lasse I might've missed it. What happens if you run this in just new made saltwater instead of tank water.
Do we know what H2O2 does to the ORP in newly made Instant Ocean?

 

[Lasse]

No - but I did not get the spike in new mixed Red Sea and new electrode.

Sincerely Lasse

 

[Dan_P]

I still think it is all well explained by trace element effects, some getting oxidized and some reduced by H2O2, and its mostly the redox active trace elements that are what is actually measured by an ORP electrode.

Lots of highly oxidizing and reducing species have little to no impact on ORP because they do not interact well with the electrode. O2 is a perfect example. H2O2 may be another.

The effect occurs with just sodium chloride which I have posted several times, though I have no idea about the purity of the sodium chloride in this internet example. Trace elements might be at play. This might easily be tested.

If trace elements are in play, dilution with RODI would diminish the effect In a dose dependent manner, right?

 

[taricha]

The effect occurs with just sodium chloride which I have posted several times, though I have no idea about the purity of the sodium chloride in this internet example.

I thought it was decided this example was due to some form of a pH effect. (h2o2 in saltwater doesn't budge the pH, so that's not an effect with h2o2 in tanks)

Thinking about the NaCl example requires me to ask all kind of dumb questions just to approach it.
Is NaCl solution buffered with repect to pH / ORP? what is ORP probe even measuring in a theoretically pure NaCl solution?

 

[Dan_P]

I thought it was decided this example was due to some form of a pH effect. (h2o2 in saltwater doesn't budge the pH, so that's not an effect with h2o2 in tanks)

Thinking about the NaCl example requires me to ask all kind of dumb questions just to approach it.
Is NaCl solution buffered with repect to pH / ORP? what is ORP probe even measuring in a theoretically pure NaCl solution?

All arm chair chemistry so far

We will need beaker work to understand what we are dealing with when a strong oxidizer causes ORP to drop. After confirming the ORP drop in a sodium chloride solution, the fun begins.

I just suggested to Randy that if we are dealing with the presence of trace elements, maybe a simple dilution with RODI will give a dose dependent change to the ORP drop. Does the dilution of aquarium water with RODI produce a dose dependent change in the ORP drop? One afternoon in the lab should provide some insight. We might just be dealing with an artifact of the ORP measurement or infinitely deep rabbit hole.

 

[taricha]

If trace elements are in play, dilution with RODI would diminish the effect In a dose dependent manner, right?

Maybe. But maybe not? If the ORP behavior has more to do with the relative amounts of metals that are reduced versus those that are oxidized by H2O2, then a straight dilution might keep the effect largely unchanged?

 

[Dan_P]

Maybe. But maybe not? If the ORP behavior has more to do with the relative amounts of metals that are reduced versus those that are oxidized by H2O2, then a straight dilution might keep the effect largely unchanged?

The size of the effect cannot stay the same upon dilution. The trace elements at some point will play out and the effect disappears or changes appearance. If you dosed H2O2 to the same sample, do you continue to observe the ORP dip unabated?

How about increasing doses of H2O2 to tank water or NaCl solution in a beaker? 1000 ppm should not behave the same as 1 ppm. IO v tank water? Does dosing trace elements have an effect? pH might have on trace element chemistry but I doubt we are are taking about changes of 0.1’s.

Glad that I did not buy an ORP probe with my new pH meter. I’d be down this rabbit hole something silly.

 

[taricha]

Glad that I did not buy an ORP probe with my new pH meter. I’d be down this rabbit hole something silly.

watch out. somebody might send you an ORP probe just to curse you with this riddle.

 

[Hans-Werner]

I have no idea about the purity of the sodium chloride in this internet example

I think at least analytical grade is necessary. "Normal" sodium chloride of food grade contains iron compounds as anticaking.

 

[Randy Holmes-Farley]

The effect occurs with just sodium chloride which I have posted several times, though I have no idea about the purity of the sodium chloride in this internet example. Trace elements might be at play. This might easily be tested.

If trace elements are in play, dilution with RODI would diminish the effect In a dose dependent manner, right?

I think it is likely the ORP probe put into "just" sodium chloride solution is still controlled by the speciation of trace metal impurities. Event the purest sodium chloride has trace metals.

Neither sodium nor chloride are likely to be impacting ORP, so, IMO, it would be more instructive to add H2O2 to very high purity DI water and see what effect it has there.

One could test the effect of added trace metals with and without H2O2, and that could be instructive (if likely predictable), but I don't think it tells us what is happening without added trace metals in either seawater or "just" sodium chloride.

I don't know that dilution tells us much.

If copper is present at 1 ppb, and you dilute to 0.1 ppb, does that alter the effect on ORP when the H2O2 is added? Maybe. Maybe not.

 

[Randy Holmes-Farley]

Just to keep perspective, what is happening on a molecular level with respect to ORP is unknown in many settings, not just in reefs with added H2O2:

The redox potential: Its use and control in biotechnology

The redox potential: Its use and control in biotechnology

This review describes the theory for and the measurement of the redox potential and the use and control of redox potential in biotechnology. The theory for the redox potential from a thermodynamic point of view is outlined and the reasons for that the measurement of...

link.springer.com

"It is concluded that although the reactions that determine the redox potential in biochemical systems are complex and almost unknown the redox potential may be a parameter which can give valuable information about the metabolism taking place in microbial cultures."

 

[Dan_P]

watch out. somebody might send you an ORP probe just to curse you with this riddle.

They will protect me from such curses - if high pitched yapping is effective.

 

[Dan_P]

I think it is likely the ORP probe put into "just" sodium chloride solution is still controlled by the speciation of trace metal impurities. Event the purest sodium chloride has trace metals.

Neither sodium nor chloride are likely to be impacting ORP, so, IMO, it would be more instructive to add H2O2 to very high purity DI water and see what effect it has there.

One could test the effect of added trace metals with and without H2O2, and that could be instructive (if likely predictable), but I don't think it tells us what is happening without added trace metals in either seawater or "just" sodium chloride.

I don't know that dilution tells us much.

If copper is present at 1 ppb, and you dilute to 0.1 ppb, does that alter the effect on ORP when the H2O2 is added? Maybe. Maybe not.

If dilution (a simple exploratory test) does not change the response of adding H2O2 , we are dealing with magic. Keep in mind that it seems everyone observes this dip. Does everyone fortuitously have the same amounts or ratios of trace elements?

If we are talking about a catalytic effect, all bets are off on precisely describing what is going on. If the dip is plain old oxidation-reduction of transition metals, we have a shot at explaining it.

We need more beaker work

 

[Dan_P]

Just to keep perspective, what is happening on a molecular level with respect to ORP is unknown in many settings, not just in reefs with added H2O2:

The redox potential: Its use and control in biotechnology

The redox potential: Its use and control in biotechnology

This review describes the theory for and the measurement of the redox potential and the use and control of redox potential in biotechnology. The theory for the redox potential from a thermodynamic point of view is outlined and the reasons for that the measurement of...

link.springer.com

"It is concluded that although the reactions that determine the redox potential in biochemical systems are complex and almost unknown the redox potential may be a parameter which can give valuable information about the metabolism taking place in microbial cultures."

Thanks for link.

Our phenomenon involves a much simpler system. Water, sodium chloride (+?) and H2O2. The phenomenon: ORP responds to this strong oxidizer like a reducing agent.

Proposed experiment: dose varying amounts of H2O2 to RODI containing various amounts of NaCl. A factorial design would work well here.

Beakers to arms!

 

[Lasse]

All of you miss one thing in this thread

I have test with RODI water, with tap water, with newly mixed saltwater and old saltwater in a bucket and not get the dip of redox. 5 ml H2O2 in 5 L of liquid every time. All have been done with new clean electrodes. The same amount of peroxide to my 300 L aquarium give a huge dip with an old electrode - but no dip at all with a new.

I have use 4 electrodes - 1 old and 3 new

This make no sense but it is a result of tests

Sincerely Lasse

 

[Hans-Werner]

This make no sense but it is a result of tests

... makes no sense except it is a biofilm-effect ...

 

[Randy Holmes-Farley]

If dilution (a simple exploratory test) does not change the response of adding H2O2 , we are dealing with magic. Keep in mind that it seems everyone observes this dip. Does everyone fortuitously have the same amounts or ratios of trace elements?

If we are talking about a catalytic effect, all bets are off on precisely describing what is going on. If the dip is plain old oxidation-reduction of transition metals, we have a shot at explaining it.

We need more beaker work

I don't agree it's magic at all.

ORP is a ratio of oxidizers to reducers and the ratio is unchanged with dilution. The Nernst equation shows this very clearly:

Nernst equation - Wikipedia

en.wikipedia.org

.

For example, if copper is the only ion impacting ORP in a solution, then the ORP is exactly determined by the ratio of Cu+ to Cu++.

That ratio is unchanged by dilution, so the ORP is also unchanged by dilution.

If hydrogen peroxide is altering the ratio of Cu+ to Cu++, is the degree of that change int he ratio determined by the absolute concentration of copper?

maybe, maybe not. Maybe it is controlled primarily by the relative oxidizing and reducing capability of the H2O2 and the copper.

It would take a much deeper understanding of the processes to even work out on paper what dilution would do, IMO.

 

[Randy Holmes-Farley]

All of you miss one thing in this thread

I have test with RODI water, with tap water, with newly mixed saltwater and old saltwater in a bucket and not get the dip of redox. 5 ml H2O2 in 5 L of liquid every time. All have been done with new clean electrodes. The same amount of peroxide to my 300 L aquarium give a huge dip with an old electrode - but no dip at all with a new.

I have use 4 electrodes - 1 old and 3 new

This make no sense but it is a result of tests

Sincerely Lasse

I do not think it disputes the trace metal hypothesis.