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

[Dan_P]

Nice.
Thinking about removal (to confirm the effect is external film/deposits).
I'm thinking toothbrush +
1) detergent
2) then if that doesn't work maybe solvent (ethanol)
3) then if that still doesn't remove the effect, acid (HCl or H2SO4)

Persulfate can oxidize organic compounds at lower temperatures. I have no idea if that would still be too punishing for the electrode. You could probably monitor nitrate production of just persulfate in solution as a way to tell at what temperature a reasonable rate of oxidation is occurring. Just a thought, not a persulfate pusher.

 

[Rick Mathew]

Nice.
Thinking about removal (to confirm the effect is external film/deposits).
I'm thinking toothbrush +
1) detergent
2) then if that doesn't work maybe solvent (ethanol)
3) then if that still doesn't remove the effect, acid (HCl or H2SO4)

I clean all of my probes with a very weak solution of HCL (.034%) and a tooth brush

15 min soak in HCL
Brush
Rinse in RODI

The .034% HCL is what I think the HCL concentration of the Hanna Probe Cleaning Solution (HI-706) is. It may have other stuff in it but I just use the HCL and make my own.

 

[taricha]

Follow up on this question...

But pre-conditioning in thiosulfate may not be as persistent - the upward ORP move when adding h2o2 may not stick around from one day to the next. Looking into that.

I put the ORP probe in straight Prime dechlorinator for ~30min. It pegged the ORP to the lowest value it could measure (-600mV or so). Then rinsed and brushed under tap water and tank water then into the tank.

H2O2 addition after being in the tank for 1.5 hours (+20mV jump) :

And then again after the probe had been in the tank water for 16 hours (+30mV jump):

So the ORP jump up with h2o2 is persistent from one day to the next at least and 2 repeat h2o2 doses after exposing the probe to a strong reducing agent.
And the ORP drop with my probe is persistent for at least a day and 3 repeat h2o2 doses after exposing the probe to a strong oxidizer (1/100 dilution of bleach, ORP goes over +700)
Below are the data runs from the bleach pre-conditioned tests that I earlier posted here in post 224.

h2o2 doses into the tank at 1hr, 16hr and just under 24 hr after probe "pre-conditioned" in bleach.

In the next couple of days I'll see if I can turn off this pre-conditioning effect by cleaning the probe. If so, then it's from the biofilms/deposits on the probe. If not - it may mean that the strong reducer/oxidizer is affecting the internal workings of the probe.

 

[taricha]

Does persulfate now cause a dip like H2O2 after treating your ORP electrode?

Trying to sort out this effect. Is it a general peroxide effect or a specific H2O2 effect?

I should have data on this tomorrow with a bleach pre-treated probe.
(my guess is no it won't drop, because even if it does the same free radical shenanigans as h2o2 - unlike h2o2, persulfate itself seems to be directly measurable by the ORP probe)

 

[taricha]

Does persulfate now cause a dip like H2O2 after treating your ORP electrode?

Trying to sort out this effect. Is it a general peroxide effect or a specific H2O2 effect?

You won't even need the annotations to tell which is the persulfate and which is the H2O2...

As said before, probe had been pre-treated with dilute bleach, then rinsed thoroughly and put in the display tank overnight before this data.

1L samples of tank water were pulled out of the tank for this, and done in a beaker with a stirrer. (essentially same results as testing in the display)

Persulfate, permanganate, and bleach added to tank water all give the same shape curves: upward flattening slopes. They have different steepness but the same general shape. Only H2O2 of these oxidizers gives the curious behavior.

 

[Lasse]

In my world - the persulfate and free chlorine are active radicals by themself - H2O2 not. The sodium persulfate will be sodium and persulfate ion directly but the breakdown of H2O2 to radical take some time and in itself not an active radical.

That´s no problem to understand - I think - but why it demand a pretreatment of bleach............?

Sincerely Lasse

 

[Rick Mathew]

I figured out how to get my ORP probe to hop back and forth between universes

All three of the following data runs are with my probe in my display tank until it stabilized with tank water, and then I added ~1ml H2O2 / 10 Gallons.
Before each run I rinsed the probe under tap water and brushed with a test tube brush.

First, a somewhat unfamiliar universe where my ORP drops slightly (-20mV) when adding peroxide to tank water.

Then I placed the probe in Universe Jumping Solution A for a couple of hours, and then rinsed in tap water and back into the tank.
Now we're back in my typical universe where the ORP increases (+20mV) when I add peroxide.

Then I placed the probe into Universe Jumping Solution B for an hour, then rinsed in tap water and back into the tank. Now we're in the universe with Lasse, Rick and the rest of the hobby where peroxide drops ORP by something on the scale of a hundred mV, followed by a multi-hour long recovery.

(Universe Jumping Solution A = my probe storage solution, Universe Jumping Solution B = 1/100 dilution of bleach in distilled water, and before the first run my probe spent the night in tank water with 25ppm sodium persulfate)

I am not able to replicate your results using my setup...I repeated it 2 times...Very Strange...The only thing I noticed that might be an issue is my Hanna Probe storage solution is about to expire...I just ordered some new...will be here Friday and I will give it another shot...only this time I think I will do the experiment with the 1L tank water...After seeing your latest results...Will save my DT from such a big hit of H2O2...I will post the charts later...Just wanted to give you a summary as soon as the results were in...Still seem to be in "parallel universes" ...Either the probes or the systems or both

 

[taricha]

but why it demand a pretreatment of bleach............?

Only because my probe after being in storage for a while doesn't act like everyone else's. After bleach (or persulfate) it does.

I am not able to replicate your results using my setup...I repeated it 2 times...Very Strange...The only thing I noticed that might be an issue is my Hanna Probe storage solution is about to expire

Try soaking your probe in Prime (or other dechlorinator) for 30 min, then rinse and into the tank to equalize. You can pull a sample out of the tank after that to dose H2O2. (See my post 243 for details of how it worked with mine.)

If results stay very different, that might point to the effect I'm seeing be more about probe construction / internal effects.

 

[Dan_P]

You won't even need the annotations to tell which is the persulfate and which is the H2O2...

As said before, probe had been pre-treated with dilute bleach, then rinsed thoroughly and put in the display tank overnight before this data.

1L samples of tank water were pulled out of the tank for this, and done in a beaker with a stirrer. (essentially same results as testing in the display)

Persulfate, permanganate, and bleach added to tank water all give the same shape curves: upward flattening slopes. They have different steepness but the same general shape. Only H2O2 of these oxidizers gives the curious behavior.

Thanks for today’s data fix!

OK, provisional idea is that H2O2 is not acting like “typical” oxidizer. DUH, right? It can cause an ORP dip rather than increase. This rabbit hole might be infinitely deep.

 

[Dan_P]

I am not able to replicate your results using my setup...I repeated it 2 times...Very Strange...The only thing I noticed that might be an issue is my Hanna Probe storage solution is about to expire...I just ordered some new...will be here Friday and I will give it another shot...only this time I think I will do the experiment with the 1L tank water...After seeing your latest results...Will save my DT from such a big hit of H2O2...I will post the charts later...Just wanted to give you a summary as soon as the results were in...Still seem to be in "parallel universes" ...Either the probes or the systems or both

Yup! Smacks of a multiverse.

 

[taricha]

Here's one more shot.
To answer a question that I'm not sure anyone was asking - is the ORP slow recovery due to the slow adjustment of the probe or due to the continued presence of the H2O2?

I took my probe in an out of a beaker of stirred tank water spiked with h2o2 over 7+ hours.

ORP dropped and stayed low in the beaker with the H2O2 for 6 hours, then I moved the probe to the display tank and it recovered quickly, then put it back into the same beaker, and it dropped back immediately, as though I had just added more h2o2.

So the slow probe recovery from peroxide seems to be due to the actual continued presence of the peroxide. (In a beaker of just stirred tank water like this test, H2O2 can last much longer than it would in a tank.)

 

[HuduVudu]

I am perhaps very late to this. If so please ignore.

Hydrogen peroxide half equation in an acidic environment:
H2O2 -> O2 + 2H+ + 2e-

Hydrogen peroxide half equation in an alkaline environment:
H2O2 + 2e- -> 2OH-

 

[Lasse]

I am perhaps very late to this. If so please ignore.

Hydrogen peroxide half equation in an acidic environment:
H2O2 -> O2 + 2H+ + 2e-

Hydrogen peroxide half equation in an alkaline environment:
H2O2 + 2e- -> 2OH-

Yes - it has been discussed as the the reason for the initial drop - but it seems like the electrode needs to be adapted at least 1 month before it shows up this behavior - or in @taricha ´s case - pretreated with bleach. and my initial test with new electrodes - pH was not a part of it. But - if possible - someone could test in different pH - CO2 is a good chose to lower the pH below 7

Sincerely Lasse

 

[Dan_P]

I am perhaps very late to this. If so please ignore.

Hydrogen peroxide half equation in an acidic environment:
H2O2 -> O2 + 2H+ + 2e-

Hydrogen peroxide half equation in an alkaline environment:
H2O2 + 2e- -> 2OH-

Thanks for this information.

@taricha observed an oxidizing event with the addition of H2O2 while most of the world observed a reducing event. Upon treating his ORP electrode with bleach, he was able to observe a reducing event. It seems the “condition” of the electrode determines which you observe.

 

[DrZoidburg]

@taricha it is in a more static environment makes sense to me.

 

[Rick Mathew]

Here's one more shot.
To answer a question that I'm not sure anyone was asking - is the ORP slow recovery due to the slow adjustment of the probe or due to the continued presence of the H2O2?

I took my probe in an out of a beaker of stirred tank water spiked with h2o2 over 7+ hours.

ORP dropped and stayed low in the beaker with the H2O2 for 6 hours, then I moved the probe to the display tank and it recovered quickly, then put it back into the same beaker, and it dropped back immediately, as though I had just added more h2o2.

So the slow probe recovery from peroxide seems to be due to the actual continued presence of the peroxide. (In a beaker of just stirred tank water like this test, H2O2 can last much longer than it would in a tank.)

Makes sense!...Good experiment

 

[Lasse]

Anyone see a pattern?

My old probe in the DT - Probe A Red circles - latest H2O2 additions. Blue circle - adjusting of light (not for this experiment). Nearly exact the same drop today as last time

My next oldest probe - nearly used a month Probe C. Last addition 28/8 result in a small drop followed of a rise. Todays addition - a laeger drop - no rise. Red circles

My third probe - B - used around 3 weeks - still erratic but have a pattern too. Red= addition of H2O2

Sincerely Lasse

 

[taricha]

Anyone see a pattern?

Seems to generally point towards the idea that over time these ORP probes develop this behavior.

I suppose the question is whether it's biofilm or slow internal changes of the probe.
Randy's reference [pdf] points out that biofouling (even of polished platinum) in seawater occurs over hours.

So why are the probes taking weeks/months to scale up to showing the effect? That's harder (but maybe not impossible) to explain as biofilm.

 

[HuduVudu]

Yes - it has been discussed as the the reason for the initial drop - but it seems like the electrode needs to be adapted at least 1 month before it shows up this behavior - or in @taricha ´s case - pretreated with bleach. and my initial test with new electrodes - pH was not a part of it. But - if possible - someone could test in different pH - CO2 is a good chose to lower the pH below 7

Sincerely Lasse

I have experimented with adding H2O2 to tank water. I was testing for PH but I noticed a rise in PH which at the time was unexpected for me. This would lend toward the 2(-OH) species reasoning.

I love this kind of stuff. It is almost like sticking a knife in an electrical socket to see what happens.

Thanks for the reply Lasse.

 

[Lasse]

I was testing for PH but I noticed a rise in PH which at the time was unexpected for me. This would lend toward the 2(-OH) species reasoning.

I have seen this once - a half a year ago - but newer after that - here is the latest additions logged against the pH curve

Sincerely Lasse