Learn the procedure for making thymolphthalein indicator solutions.
Thymolphthalein (C28H30O4) is a phthalein dye that is used as an acid-base (pH) indicator. It comes in a white powder that is synthesized from thymol and phthalic anhydride.
Its pH transition range is 9.3–10.5, and its endpoint is a blue color shift. Its transition range is around pH 9.3–10.5; its endpoint is colorless to blue. Thymolphthalein is commonly used as a weak acid and strong base indicator and is also used as a laxative and for disappearing ink.
How to prepare thymolphthalein indicator for titration:
- Weigh accurately 0.1 gm of thymolphthalein and pour it into a 100.00 ml volumetric flask containing 50.00 ml of 95% ethanol, mix it.
- Once it is dissolved, dilute to 100.00 ml with water.
- The concentration of the prepared solution is about 1 g/L.
Thymolphthalein has a pKa of 9.9 and the pH range is 9.3 to 10.5. It is colorless (below pH 9.3), in acidic solutions, while in a basic condition (above pH 10.5) it turns blue. In acid-base titrations, is frequently used as an indicator.
References:
- Wikipedia contributors. (2021, December 6). Thymolphthalein. In Wikipedia, Available Here:
- Law.resource.org. 2022. [online] Available Here:
- Dr John Elfick, j., 2022. Learn how to prepare useful acid-base indicators. Uq.edu.au. Available Here:
- Sabnis, R. W. (2008). Handbook of Acid-Base Indicators. Boca Raton, FL: CRC Press.
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