Btb

[The_simpsons]

im not sure what it is called in english, but the swedish short name for it is BTB, and maybe its the same in english, its a yellow-red liquid, that indicates pH, if you add to a acidic solution it turns yellow-red, if its added to a neutral solution it becomes green or if you add it to a alkaline solution it becomes blue. my question is, how is the chemical structure of the chemical, and what makes it change colour depending on acidic, neutral or alkaline solutions?

[raivo]

This is Bromothymol Blue.

[ecoli]

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