How to Make Thymolphthalein pH Indicator

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By
Anne Marie Helmenstine, Ph.D.
Anne Marie Helmenstine, Ph.D.
Chemistry Expert
  • Ph.D., Biomedical Sciences, University of Tennessee at Knoxville
  • B.A., Physics and Mathematics, Hastings College
Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.
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Updated on January 10, 2020

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

Procedure

  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:

Sources

  • 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. 
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Helmenstine, Anne Marie, Ph.D. "How to Make Thymolphthalein pH Indicator." ThoughtCo, Feb. 16, 2021, thoughtco.com/thymolphthalein-indicator-solution-608148. Helmenstine, Anne Marie, Ph.D. (2021, February 16). How to Make Thymolphthalein pH Indicator. Retrieved from https://www.thoughtco.com/thymolphthalein-indicator-solution-608148 Helmenstine, Anne Marie, Ph.D. "How to Make Thymolphthalein pH Indicator." ThoughtCo. https://www.thoughtco.com/thymolphthalein-indicator-solution-608148 (accessed March 30, 2023).