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

[Randy Holmes-Farley Verified Community Expert]

What you talkin bout Willis? Heeee

Just didn’t want folks reading that to think it was some sort of explanation.

 

[Dr. Dendrostein]

Just didn’t want folks reading that to think it was some sort of explanation.

We'll some see it half full other half empty. ...
But yes, I see, says the blind man. I see your point. One of the decades, the student will become the master. ...one of these decades.

 

[taricha]

I am very familiar with chemistry and ORP, and there is no simple chemistry explanation of how adding an oxidizer lowers ORP.

Is there a possibility this is simply a measurement artifact of some devices?
In trying to replicate it, I find the boring correct direction. H2O2 increases the ORP immediately and it stays increased for at least the hour or two I paid attention.
In tank, in beakers, whatever. I add h2o2 and the ORP goes up. I'm doing 1ml/10L of standard 3% peroxide. The increase is around 30-40mV.
I'll try again with the more typical 1mL/10 gal, in case my higher dose is overwhelming the potential effect.

The only difference I can think of is that my ORP sensor is not from an aquarium company. It's from Vernier, an educational science supplier.

 

[Randy Holmes-Farley Verified Community Expert]

Is there a possibility this is simply a measurement artifact of some devices?
In trying to replicate it, I find the boring correct direction. H2O2 increases the ORP immediately and it stays increased for at least the hour or two I paid attention.
In tank, in beakers, whatever. I add h2o2 and the ORP goes up. I'm doing 1ml/10L of standard 3% peroxide. The increase is around 30-40mV.
I'll try again with the more typical 1mL/10 gal, in case my higher dose is overwhelming the potential effect.

The only difference I can think of is that my ORP sensor is not from an aquarium company. It's from Vernier, an educational science supplier.

I'm not sure how it could be an artifact of the probes to send the effect in a different direction.

That said, ORP is super complicated because only certain chemicals are able to interact with the probe. It would be a little like measuring the temperature of a gas or liquid by measuring only the temperature of one of the component molecules, and it is more complicated because most chemicals in the tank are not in redox equilibrium, meaning the different components of the gas might actually be at different temperatures (if it were, O2 and organics like proteins could not coexist).

One certainly could overwhelm an effect such as the possibility I suggested relating to bacteria.

 

[taricha]

I'll try again with the more typical 1mL/10 gal, in case my higher dose is overwhelming the potential effect.

I repeated it at the more typical 1mL h2O2 per 10 Gallons. Still the ORP does the boring correct thing and goes up.

I'm not sure how it could be an artifact of the probes to send the effect in a different direction.

I looked at the specs on mine (Vernier) and more typical ones in the hobby. It seems like they are using the same materials Ag/AgCl and Pt, so unlikely as you say.

My best guess here is that bacteria effect you describe may be the h2o2 interacting with the biofilm growing on the probe itself. Mine doesn't stay in-tank and is clean. Others are in-tank 24/7.

I'm leaving my probe in the tank for a week or two and we'll see if I have better luck replicating the effect.

 

[Randy Holmes-Farley Verified Community Expert]

Thanks for the informative experiments!

 

[chicago]

Just catching this thread.. I have system with about 600 gallons.. planned on dosing 3ml per 10 gallons so like 180 ml a day.. but thought I would start out slow.. even when I dose on 20 ml on this water volume I get a huge drop also.. Kinda crazy... 398 to like 198 ....

 

[Lasse]

@Randy Holmes-Farley
May this screenshots give some explanations to this question? - from here

Here is another source claiming the same

​

Sincerely Lasse

 

[Lasse]

Or this - from here

Sincerely Lasse

 

[Lasse]

I also seen an explanation when the adding of H2O2 could start a chain of active radicals that could initiate an ORP drop - here

In a case I overdose H2O2 into my tank (by mistake) I saw a huge drop in ORP - taking a day before it was up in normal levels again and also detect directly response from many of my corals - the polyps just disappear for a day or two - indicating that something irritated them - maybe active oxygen radicals.

Sincerely Lasse

 

[taricha]

The H2O2 decomposition in the presence of platinum is one that produces O2.
Which according to @Lasse above info is h2o2 acting as a reducing agent. So measurement with the ORP probe (platinum electrode) in aquarium water is using h2o2 as a reducer at the site of the electrode?

 

[Lasse]

ORP is not platinum as I know - it is the conductivity probe in GHL that´s is platinum. its true that i have my conductivity probe close to my Oxydator but i have not seen any change when I move the oxydator to that apartment - earlier I had the oxydator downstream my electrodes. In some way its the same now because my outflow (from the aquarium) is directly flushing my electrodes - meaning that it is mainly water from the tank that hit them.

Sincerely Lasse

 

[Randy Holmes-Farley Verified Community Expert]

This may be the explanation, but I don't see a clear detailed molecular process to do it.

I understand there are some circumstances where H2O2 can act as a reducing agent, but I don't see a clear way that ends up at lower ORP.

For example, if it could somehow reduce Fe+++ to Fe++, that would lower ORP. But I don't think it will do that. It is well known to do the opposite: oxidize Fe++ to Fe+++.

Iron and Metals Removal with H2O2 | USP Technologies

 

[Randy Holmes-Farley Verified Community Expert]

ORP is not platinum as I know - it is the conductivity probe in GHL that´s is platinum. its true that i have my conductivity probe close to my Oxydator but i have not seen any change when I move the oxydator to that apartment - earlier I had the oxydator downstream my electrodes. In some way its the same now because my outflow (from the aquarium) is directly flushing my electrodes - meaning that it is mainly water from the tank that hit them.

Sincerely Lasse

ORP can be platinum.

Laboratory ORP Sensor

Accurate and reliable sensors that measure the Oxidation Reduction Potential (ORP).

www.mt.com

"METTLER TOLEDO offers platinum, silver and gold ORP sensors to best support your application. "

 

[taricha]

Yeah, oops. Though some are Pt, mine and most other ORP are Ag/AgCl.

 

[Randy Holmes-Farley Verified Community Expert]

Yeah, oops. Though some are Pt, mine and most other ORP are Ag/AgCl.

Mine were platinum.

The AgCl part is the reference part, which sometimes is in a different electrode entirely (my case, for example):

Anatomy of an ORP sensor

ORP sensors work by measuring the electrical potential (voltage) between two electrodes in contact with water. Both electrodes are often contained in a single unit called a combination electrode. One electrode is called the indicator electrode, and it is usually made of platinum (other materials such as gold or graphite are also sometimes used).

The other electrode is called the reference electrode. The reference electrode is usually made of silver and silver chloride (Ag/AgCl electrodes), although electrodes made of mercury and mercury chloride (called “calomel electrodes”) are sometimes used. This electrode contains a filling solution containing potassium chloride.

Electrons from the water interact with both electrodes, creating a voltage between them that is read by the meter.

How to test ORP

Oxidation-Reduction Potential (ORP) is measured by inserting an ORP sensor into water. This can be either a handheld sensor or it can be built into a system. The meter then reads the electrical potential (voltage) from the sensor, and it may appl...

support.aperainst.com

 

[taricha]

One electrode is called the indicator electrode, and it is usually made of platinum (other materials such as gold or graphite are also sometimes used).

The other electrode is called the reference electrode. The reference electrode is usually made of silver and silver chloride (Ag/AgCl electrodes),

Thanks.
And if both silver and platinum decompose h2o2 producing o2 at both the indicator and reference electrode, then... ??? I have a headache.

 

[Lasse]

Yes but it does not measure O2 - is the ORP - however - maybe the answer is here. I normally do not have any drop - when the oxidator dose normally - but when I have filled it up and some residues on the flask get down in the sump or if I dose manually - I get the drop. Could it be that when the ORP electrode get a fast contact - it just catalyze oxygen at the plates - and after a while it will reach equilibrium and it works as intended again - just a crazy idea. I know of experiences that redox probes do not like fast changes - it takes long time before it has adapted back to my aquarium water if I take it up for cleaning as an example.

Sincerely Lasse

 

[maciejPL]

ORP drops because h202 is not oxidizer but a reducing agent. Acids are oxidizers. This misconception comes from this old way of thinking "The term oxidation was first used by Antoine Lavoisier to signify the reaction of a substance with oxygen. Much later, it was realized that the substance, upon being oxidized, loses electrons, and the meaning was extended to include other reactions in which electrons are lost, regardless of whether oxygen was involved."

H202 is donor of electrons, so reducing agent. Acids - hydrogens, pick up electrons, so they are oxidizers.

Rusting involves acids, which is also oxidation process..

I also propose to read science about grounding, how body picks up electrons from Earth and restores Zeta potential of erythrocytes - their negative charge and they start to repel eachother again https://www.groundology.pl/badania-naukowe

same deal with alkaline water, it is source of electrons that makes red blood cells repel
Yet here is some other explanation that apparently it can be both, oxidizer and reducing agent

11.20: Substances Which Are Both Oxidizing and Reducing Agents

Previous sections have looked at common oxidizing and reducing agents. This section investigates substances that can act either oxidizing or reducing agents.

chem.libretexts.org

 

[Randy Holmes-Farley Verified Community Expert]

Welcome to Reef2Reef!

ORP drops because h202 is not oxidizer but a reducing agent. Acids are oxidizers. This misconception comes from this old way of thinking "The term oxidation was first used by Antoine Lavoisier to signify the reaction of a substance with oxygen. Much later, it was realized that the substance, upon being oxidized, loses electrons, and the meaning was extended to include other reactions in which electrons are lost, regardless of whether oxygen was involved."

Unfortunately, you are not providing any clarification of how it causes a drop in ORP (if you can, please provide an actual reaction that will lower ORP, not just by claiming that there are circumstances where it acts as a reducing agent). That may well be the explanation, as we discussed earlier in this thread, but it is not at all clear how that would be working (e.g., what is reduced and what is oxidized)).

FWIW, I know what an oxidation reaction is.

the known reaction of hydrogen peroxide and ferrous iron is a redox reaction that oxidizes the iron and reduces the hydrogen peroxide (like any oxidation does), and that process will raise ORP:

Iron and Metals Removal with H2O2 | USP Technologies

"Hydrogen peroxide can be used to quickly oxidize soluble ferrous iron to ferric (Fe+3), forming a rapidly settling ferric hydroxide floc"