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New Contributor

Trying to understand redox indicators

Hi There,

My previous question didn’t attract any responses, so I’m going to try and rephrase the question. Im trying to learn about pH indicators to use in a product I’d like to develope, but I’m afraid my understanding of chemistry is making it difficult for me.

im looking for some kind of pH indicator that can be added to an organic solvent, or even water, that will react to oxygen when later exposed. I’ve read about redox indicators but these seem to revert to their reduced form over time, where as I’m trying to find a type of indicator can be added and activate once and permanently. The reaction has to be instant, or near to. Ideally, I’d like for it to be naturally clear in its reduced form, just off of Wikipedia these compounds work as redox agents but I know nothing about their use or viability:

2,2'-bipyridine (Ru complex)+1.33colorlessyellow
Nitrophenanthroline (Fe complex)+1.25cyanred
N-Phenylanthranilic acid+1.08violet-redcolorless
1,10-Phenanthroline iron(II) sulfate complex (Ferroin)+1.06cyanred
2,2`-Bipyridine (Fe complex)+0.97cyanred
5,6-Dimethylphenanthroline (Fe complex)+0.97yellow-greenred
Sodium diphenylamine sulfonate+0.84red-violetcolorless
Sodium 2,6-Dibromophenol-indophenol

or Sodium 2,6-Dichlorophenol-indophenol

Sodium o-Cresol indophenol+0.62+0.19bluecolorless
Thionine (syn. Lauth's violet)+0.56+0.06violetcolorless
Methylene blue+0.53+0.01[2]bluecolorless
Indigotetrasulfonic acid+0.37-0.05bluecolorless
Indigotrisulfonic acid+0.33-0.08bluecolorless
Indigo carmine

(syn. Indigodisulfonic acid

Indigomono sulfonic acid+0.26-0.16bluecolorless
Safranin T+0.24-0.29red-violetcolorless
Neutral red+0.24-0.33redcolorless

What is the difference between pH independent and dependent?

Ive also learned that once these solutions “set” they will no longer function — does that mean they won’t revert back to a reduced state or that they will permenantly stay in their oxidized state?

Thank you, I look forward to any and all responses.

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3 Replies
New Contributor

Re: Trying to understand redox indicators

In answer to your one question, something that is pH independent means, essentially, that it works across the spectrum of acid and base content.  If the process were pH dependent, then the acid/base content has a direct impact on the process.

As to your problem, what exactly are you trying to accomplish?  What type of process are you looking at in which one uses the pH as an indicator?

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New Contributor

Re: Trying to understand redox indicators

I just want it to change color, to indicate where the adhesive has separated, exposing it to air and changing color. Like two pieces of plastic, a solvent glue would be rolled on (with the pH indicator mixed into it) to a sheet and pressed onto another. Once set, if they separated I would like the glue/compound to change color....

hopefully thats makes more sense

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Contributor III

Re: Trying to understand redox indicators

Dear Jason,

I don't have a direct solution, but your questions are moving in the right direction.  First of all, define what you want to happen.  I think that you are short-circuiting the process by mentioning pH indicators.  That may or may NOT be part of a solution.  In any case it may be irrelevant to the cause-effect sequence that you are really interested in.  You want some method of indicating the separation of two adhesive layers.  NOW some chemists may begin to be able to offer suggestions.  Further data needed would be the types of substrates, adhesive compounds, and whether the indication should remain even if the layers re-adhere.

A very important part of research development is to start with the END in mind, and never get stuck on one particular pathway or mechanism!

Best regards,