Thymol blue

Thymol blue is an indicator. Its chemical formula is C27H30O5S. Thymol blue has three color stages in an aqueous solution. It is insoluble in water but soluble in alcohol and dilute alkali solutions.

There are 11 test tubes containing the pH indicator thymol blue and a solution. The solutions are between pH 2 and 12. The solution at pH 2 is red. The solutions between pH 3 to 7 are yellow. The solution at pH 8 is light green. The solution at pH 9 is dark green. The solutions at pH 10, 11, and 12 are dark blue.

Figure: The color of thymol blue in solution at various pH levels. At pH 1.2 - 2.8 the solution is red. Above a pH of 2.8 - 8 the solution is yellow. At pH 8 - 9.6 the solution changes color from yellow to blue. Above a pH of 9.6 the solution is dark blue.