Learn the procedure for making phenol red 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 phenol red indicator for titration:
- Weigh accurately 100 mg of phenol red and pour it into a 100.00 ml volumetric flask containing 02.82 ml of 0.05N NaOH solution and 20.00 ml of 95% ethanol, warm it.
- After the solution has been effected, dilute to 100.00 ml with distilled water.
- The concentration of the prepared solution is about 1 g/L.
Phenol red (C19H14O5S) is a synthetic phenolic compound also known as phenolsulfonphthalein or PSP, which acts as a weak acid in a solution. Phenol red exists as a red crystal that is stable in air, it is a water-soluble dye used as an acid pH indicator in different medical and cell biology tests.
Phenol red has a pKa of 8.0 and the pH range is 6.8 to 8.2. In an acidic medium (below pH 6.8) it turns yellow, while in a basic condition (above pH 8.2) it turns bright pink.
Bromothymol blue, thymol blue, bromocresol purple, thymolphthalein, and phenolphthalein are all indicators that have a similar structure to phenol red.
References:
- Wikipedia contributors. (2022, January 1). Phenol red. 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:
- Sabnis, R. W. (2008). Handbook of Acid-Base Indicators. Boca Raton, FL: CRC Press.
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