Bromothymol blue is a pH indicator: it shows acids and bases by changing color. When you add acid, bromothymol blue turns yellow; when you add a base (like sodium sulfite), it turns blue. Green means neutral (like water).

What does bromothymol blue react with?

It's used to watch changes in pH; photosynthesis, where carbon dioxide is used up; and respiration (carbon dioxide is produced). This works because bromothymol blue can be deprotonated above a pH of 7.1, which creates a blue color, while the protonated form, below a pH of 7.1, is a yellow compound.

Is bromothymol blue a base or acid?

Bromothymol blue is an acidic pH chromoionophore where acid to base change corresponds to its neutral to anionic form, respectively. For this reason it can be electrostatically immobilized on the surface on anion-exchanger resin like Amberlite IRA 401. Solutions of different concentration of the indicator were used.