Relationship Between H2O2 & Redox (ORP) . . . Help with Explanation?

[maciejPL]

There is no reaction , otherwise it would be heat expelled i think. Unless there are some pollutants and miniscule oxidation occurs. ORP meter measures net charge, and h202 introduces more negatively charged particles i think.

p.s. i used to drop some h202 30% drops on mine shirt amazing how it heats up....burning holes

 

[Randy Holmes-Farley]

There is no reaction , otherwise it would be heat expelled i think. Unless there are some pollutants and miniscule oxidation occurs. ORP meter measures net charge, and h202 introduces more negatively charged particles i think.

p.s. i used to drop some h202 30% drops on mine shirt amazing how it heats up....burning holes

Sorry, this is ALL not correct.

Reactions do not all make heat. Some soak up heat. In either case, in an aquarium you'd never notice either way at these dilutions. Too little to detect.

ORP certainly does not measure net charge. All of the ions in seawater are charged already. There is always an equal number of positive and negative charges in seawater.

You might find it useful to review this article on what ORP is actually measuring:

ORP and the Reef Aquarium - Reefkeeping.com

 

[Lasse]

@Randy Holmes-Farley - Do you know any other method to measure ORP besides electrodes consisting partly of metals? Just in order to make it possible to rule out a secondary effect at the measuring point?

Sincerely Lasse

 

[maciejPL]

asu

We are talking about oxidation, and oxidation is burning. Burning creates heat. I will read article, but still all the supposed complexity of "ORP" , measurment is still basic thing - Voltage Potential, either positive or negative. It reflects balance of positive nucleons with available free electrons.

If number of positive ,mostly H+ or hydronium ions, matches number of free electrons, ORP is 0

P.S. this discussion board is very tasteful and pretty

 

[Randy Holmes-Farley]

@Randy Holmes-Farley - Do you know any other method to measure ORP besides electrodes consisting partly of metals? Just in order to make it possible to rule out a secondary effect at the measuring point?

Sincerely Lasse

I'm not aware of any others that are commercially available.

 

[Randy Holmes-Farley]

We are talking about oxidation, and oxidation is burning. Burning creates heat. I will read article, but still all the supposed complexity of "ORP" , measurment is still basic thing - Voltage Potential, either positive or negative. It reflects balance of positive nucleons with available free electrons.

If number of positive ,mostly H+ or hydronium ions, matches number of free electrons, ORP is 0

P.S. this discussion board is very tasteful and pretty

Please read the article before continuing this discussion. We are getting side tracked with unrelated and incorrect assertions.

As an aside, please keep the following in mind...

1. Combustion is a redox reaction (involving both an oxidation and a reduction), but not all redox reactions would be called combustion. For example:

Ag+ + Cu+ --> Cu++ + Ag

Is a redox reaction with the copper ion being oxidized and the silver ion being reduced. It does not involve anything that would be called combustion.

2. Combustion, even with oxygen in the gas phase, does not always give off heat. Sometimes it takes up heat. Combustion (Oxidation) of N2 with O2 to NO is an example of an endothermic combustion.

 

[maciejPL]

Sorry, this is ALL not correct.

Reactions do not all make heat. Some soak up heat. In either case, in an aquarium you'd never notice either way at these dilutions. Too little to detect.

ORP certainly does not measure net charge. All of the ions in seawater are charged already. There is always an equal number of positive and negative charges in seawater.

You might find it useful to review this article on what ORP is actually measuring:

ORP and the Reef Aquarium - Reefkeeping.com

Yes exotermic and endotermic, but u see with burning,when there is transfer of electrons from higher energy state to lower, there is reduction in one place and increase in other place. Transfer of energy in exotermic reaction.

Burning/oxidation is exotermic reaction and we are talking about redox reactions.

2. Combustion, even with oxygen in the gas phase, does not always give off heat. Sometimes it takes up heat. Combustion (Oxidation) of N2 with O2 to NO is an example of an endothermic combustion.

Then it is not combustion by definition which is exotermic https://en.wikipedia.org/wiki/Combustion

Combustion, or burning,[1] is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and anoxidant,

 

[Randy Holmes-Farley]

Yes exotermic and endotermic, but u see with burning,when there is transfer of electrons from higher energy state to lower, there is reduction in one place and increase in other place. Transfer of energy in exotermic reaction.

Burning/oxidation is exotermic reaction and we are talking about redox reactions.



Then it is not combustion by defitiniot which is exotermic https://en.wikipedia.org/wiki/Combustion

There's no need to lecture me on what these terms mean. I have a PhD in physical chemistry from Harvard University.

Combustion is not always exothermic. Usually it is. Not always.

Combustion ("burning") of N2 with O2 at high temperatures is endothermic. That is a simple fact.

Redox reactions cover far more than "combustion", which is really unrelated to the topic at hand: ORP in seawater.

Let's get back to the topic of why hydrogen peroxide lowers ORP in seawater. I'm interested to understand why, and so far, I've not seen convincing ideas about what does it, aside from the possibility I mentioned earlier of the hydrogen peroxide killing and breaking open cells with a low redox interior.

Yes, it might possibly act as a reducing agent (with something else oxidizing it), but what would do that which actually lowers ORP in seawater? I do not see any chemicals that fit that description.

 

[maciejPL]

There's no need to lecture me on what these terms mean. I have a PhD in physical chemistry from Harvard University.

Really ? Sounds fancy.

Combustion ("burning") of N2 with O2 at high temperatures is endothermic. That is a simple fact.

But how if definition of burning is exothermic reaction ? There is also a process called - decomposition.

 

[Randy Holmes-Farley]

Really ? Sounds fancy.


But how if definition of burning is exothermic reaction ? There is also a process called - decomposition.

Yes, it is very fancy.

There's no point in debating the definition of chemistry terms, especially since none of these comments about heat bear in any way on the impact of hydrogen peroxide on ORP in reef aquaria.

 

[Lasse]

aside from the possibility I mentioned earlier of the hydrogen peroxide killing and breaking open cells with a low redox interior.

This should be rather easy to confirm or role out. Jus put H2O2 in new mixed saltwater with no organic content. I´ll do that experiment when I get the time, But the reaction is fast - the dip comes after one or two minutes after adding H2O2

Sincerely Lasse

 

[maciejPL]

I think in order to solve this it would be useful perhaps to write down stechiometric redox chemical reactions with detailed depiction on how exactly electrons switch which orbital from one atom to the other. As a Ph.D , can You tell me if such a method perhaps exists ?

To get as close to quantum mechanism of these reactions as possible.

 

[Randy Holmes-Farley]

I think in order to solve this it would be useful perhaps to write down stechiometric redox chemical reactions with detailed depiction on how exactly electrons switch which orbital from one atom to the other. As a Ph.D , can You tell me if such a method perhaps exists ?

To get as close to quantum mechanism of these reactions as possible.

I can easily do that, IF we knew what it was reacting with that caused ORP lowering, and how exactly. There are many complications, including H2O2 breaking down first, then those new species reacting:

Reaction kinetics of hydrogen peroxide with copper and iron in seawater

https://pubs.acs.org/doi/10.1021/es00162a012

The oxidation of iron and copper in seawater is relatively easy:

Fe++ + H2O2 --> Fe+++ + OH + OH- (slow)
Fe++ + OH ---> Fe+++ + OH- (fast)


Cu+ + H2O2 --> Cu++ + OH + OH- (slow)
Cu+ + OH ---> Cu++ + OH- (fast)


The possible ways of reduction are more complicated, and for iron, it is not observed. For copper, some reaction may be observed, depending on the forms of copper actually present, but it does not seem a dominant reaction

H202 ---> + H+ + HO2-
Cu++ + HO2- ---> Cu+ + HO2
HO2 ---> H+ + O2-
Cu++ + O2- ---> Cu+ + O2

They say:

"Cu++ reduction is more difficult to assess because the speciation in seawater is controlled by poorly characterized organic chelators. Recent evidence indicates that in surface oligotrophic seawater Cu2+kee/Cu2+,d 1 X (39,40). Using this to obtain a pseudo-first-order rate for Cu(I1) reduction indicates 1-2% of total Cu present as Cu(1) at M H202 (40). Recent measurements of Cu(1) produced by sunlight irradiation of seawater are 6-10 times higher than this, indicating other reduction processes are more important"

"No observable Fe++ reduction by peroxide occurred in the pH range 7-8,"

 

[maciejPL]

I think Lasse gave an answer in this picture, it is not about h202 reacting with anything, which it of course does if it has something to react with, but about supplying addition electrons to the solution like in the picture below.
These electrons just float between ions and add up to net charge of a solution, lowering ORP.

edit 1 : and it is actually good if h202 has nothing to react with because free floating electrons are not picked up and used up, if You want to maintain lower orp.

 

[Randy Holmes-Farley]

I think Lasse gave an answer in this picture, it is not about h202 reacting with anything, which it of course does if it has something to react with, but about supplying addition electrons to the solution like in the picture below.
These electrons just float between ions and add up to net charge of a solution, lowering ORP.

That statement doesn't make sense.

Did you read the article yet? ORP has nothing to do with net charge.

When a reaction is shown giving a loose electron, that is a half reaction, and the other half is not shown BUT MUST BE THERE. The electron must go somewhere, immediately. The free electron is not altering ORP, and it doesn't exist in water. What it ends up attached to can alter ORP. The free electron simply shows that it is acting as a reducing agent, not what is actually happening.

My question is, and what I'm skeptical about, is what exactly that electron is ending up attached to that lowers ORP (if one assumes this hypothesis of it acting as a reducing agent is correct).

Note that earlier experiments in this thread did not show an ORP drop, but a rise.

 

[Randy Holmes-Farley]

Maybe the ORP lowering effect is from reduction of Cu++ to Cu+, as suggested above, overriding the oxidation of other trace elements such as Fe+++. If that's the case, the effect people observe may depend a lot on the type and amount of copper forms already present before addition.

https://www.int-res.com/articles/meps/178/m178p145.pdf

"For example, cupric ion is reduced by hydrogen peroxide in seawater; thermodynamic calculations indicate that Cu(1) varies from 10 to 25% of the total dissolved inorganic copper over the hydrogen peroxide concentration increase in these experiments (Moffett & Zika 1983). Because Cu(1) forms a stable complex with chloride, it can persist for many hours before oxidation by O2 (Moffett & Zika 1983). "

Also, it might possibly be manganese related.

"Reduction and subsequent dissolution of particulate MnO2 by concentrations of hydrogen peroxide in the lO-7 M range has been proposed by Sunda et al. (1983)."

 

[maciejPL]

Maybe the ORP lowering effect is from reduction of Cu++ to Cu+, as suggested above, overriding the oxidation of other trace elements such as Fe+++. If that's the case, the effect people observe may depend a lot on the type and amount of copper forms already present before addition.

https://www.int-res.com/articles/meps/178/m178p145.pdf

"For example, cupric ion is reduced by hydrogen peroxide in seawater; thermodynamic calculations indicate that Cu(1) varies from 10 to 25% of the total dissolved inorganic copper over the hydrogen peroxide concentration increase in these experiments (Moffett & Zika 1983). Because Cu(1) forms a stable complex with chloride, it can persist for many hours before oxidation by O2 (Moffett & Zika 1983). "

Also, it might possibly be manganese related.

"Reduction and subsequent dissolution of particulate MnO2 by concentrations of hydrogen peroxide in the lO-7 M range has been proposed by Sunda et al. (1983)."

To test if metals are a factor in this, we could try to use distilled/demineralized water, add h202 and measure ORP.

I don`t have ORP meter somebody else can do it.
I am looking for a paper on this, but can`t find anything.

We will then exclude that a chemical reaction is responsible for ORP drop.

 

[Lasse]

If we get a drop even in RO water - we can´t still not rule out metals importance because it can be a reaction taking place at the probes metals part. However if we get no reaction - we no that it is not the probe that trick us. I will put up an experiment - However - I do not expect any drop because the H2O2 is rather stabil in RO water (it is possible to dilute)

I will set up an experiment with this - I have brand new redox probes at home. If no reaction - I can ad different metals - @Randy Holmes-Farley which should I start with (I have Tritons trace metals at home) ?

Sincerely Lasse

 

[maciejPL]

Reverse osmosis removes minerals ? That is not healthy, minerals are very important and if You drink demineralized water You will flush out minerals already in Your body.

Don`t You have some bought demineralized or distilled water at home ? I Do but i don`t have orp meter

 

[Lasse]

RO water is the standard water most of us use when we mix our saltwater. RO water/demineralized (deionized) and distalled water is rather equal to each others according to mineral and ion content.

My water´s conductivity is around 3 µS/cm.

Sincerely Lasse