Science, Tech, Math › Science How to Make Thymolphthalein pH Indicator Share Flipboard Email Print Dave White / Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By 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. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated 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 thymolphthalein95% ethanoldistilled water Procedure Dissolve 0.04 g thymolphthalein in 50 mL of 95% ethanol.Dilute this solution to 100 mL with distilled water. Thymolphthalein Projects Thymolphthalein is used to make disappearing ink and in other pH indicator projects: Make Disappearing InkMake Colored Soap BubblesPatriotic Colors Electrolysis Demo 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.