How to Make Thymolphthalein pH Indicator

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Thymolphthalein is an acid-base indicator that changes color from colorless to blue. Below a pH of 9.3-10.5, it s colorless. Above this range, it is blue. These are instructions for making 100 mL of thymolphthalein pH indicator solution.

Thymolphthalein Materials

  • 0.04 g thymolphthalein
  • 95% ethanol
  • distilled water


  1. Dissolve 0.04 g thymolphthalein in 50 mL of 95% ethanol.
  2. Dilute this solution to 100 mL with distilled water.

Thymolphthalein Projects

Thymolphthalein is used to make disappearing ink and in other pH indicator projects:


  • Hubacher, M.H.; Doernberg, S.; Horner, A. (1953). "Laxatives: Chemical Structure and Potency of Phthaleins and Hydroxyanthraquinones." J. Am. Pharm. Assoc. 1953;42(1):23-30.