Bromothymol Blue is a pH indicator.
Bromothymol blue acts as a weak acid in a water solution. It can thus be in protonated (dissolved in acid) or deprotonated (dissolved in an alkaline) form, appearing yellow or blue respectively. It is bright aquamarine or greenish-blue in a neutral solution. Bromothymol blue may be used for observing photosynthetic activities, or as a respiratory indicator (turns yellow as Carbon Dioxide is added). A common demonstration of Bromothymol Blue's pH indicator properties involves exhaling through a tube into a neutral solution of Bromothymol Blue. As carbon dioxide is absorbed from the breath into the solution, forming carbonic acid, the solution changes color from green to yellow.
In concentrated HCl, Bromothymol Blue turns pink, but in normal acids, it turns yellow. It will remain green in a neutral solution anywhere between pH 6.0 - 7.6 Bromothymol Blue, hence its name, turns blue in all alkalines above pH 7.6 .
|Magenta||< 0||Concentrated Hydrochloric acid|
|Yellow||0 - 6||Lemon Juice|
|Green||6 - 7.6||Water|
|Blue||> 7.6||Washing-up liquid|