[Ulagatin]

Hi all,

This is my first post on this forum. I'm in Year 12 in Australia, and studying pre-tertiary chemistry this year. However, my strongest suits are mathematics and physics respectively, so please forgive me for a weak chemistry background. I have just recently become interested in chemical theory! 

I do not need to know this for study purposes, but I have a question out of curiosity. How and why do pH indicators work? Take for example, the indicator Thymol blue. Does the indicator undergo a redox reaction with the solution it is testing? What is the chemical structure of such an indicator, and is the colour produced a result of the quantum model of the atom (i.e. excitation of the electrons in some form)? What reaction is undergone by the indicator in solution?

What occurs when equilibrium is established? I have not yet studied equilibrium, so if this is relevant, I would need some background into the theory.

Any help in understanding this question would be greatly appreciated, and I understand it is probably well above my current level of understanding. Regardless, I am very curious and would love to delve into this further! 

Thanks in advance. Great forum too!

Cheers,
Ulagatin

[Borek]

Different forms present in different pH have different colors, no need for redox.

http://en.wikipedia.org/wiki/Phenolphtalein

http://www.titrations.info/acid-base-titration-indicators

[Ulagatin]

Thanks Borek. I've seen you around on physicsforums.com - I thought your name was familiar. 

Those links help, I will need to read up on the theory behind equilibrium constants etc, but I like that second link for going through the mathematical details.

Ulagatin