Learn the procedure for making thymol blue indicator solution.
The compound that change color when exposed to acidic or basic solutions are called indicator. Color indicators are commonly used to measure pH and are added to the reaction mixture to identify the titration endpoint/equivalence point.
Most pH indicators are weak acids or bases. For titration, you must select a pH indicator that changes color only at the equivalence point.
How to prepare thymol blue indicator for titration:
- Weigh accurately 0.1 g of thymol blue and pour it into a 100 ml volumetric flask containing 2.15 ml of 0.05 N NaOH solution and 05.00 ml of 95% ethanol, warm it.
- After the solution has been effected, add 25.00 ml of 95% ethanol and dilute to 100 ml with distilled water.
- The concentration of the prepared solution is about 1 g/L.
Thymol blue (Thymolsulfonephthalein- C27H30O5S) is a crystalline powder that is brownish-green or reddish-brown in color and is used as a pH indicator. It has a pKa of 0.8 and pH ranges of 1.2-2.8 and 8.0–9.6. At pH 1.2–2.8, it changes from red to yellow, while at pH 8.0–9.6, it transitions from yellow to blue.
Thymol blue is a weak acid that is soluble in alcohol and dilute alkali solutions but not in water. It is also usually a component of the universal indicator.
References:
- Wikipedia contributors. (2021, December 12). Thymol blue. In Wikipedia, The Free Encyclopedia. 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:
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