Learn the procedure for making phenolphthalein indicator solutions.
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.
Phenolphthalein (C20H14O4) is a chemical compound often written in shorthand notation as "HIn" or "phph" that belongs to the phthalein family. Phenolphthalein can be formed by condensation of phthalic anhydride with two equivalents of phenol under acidic conditions.
It comes in a yellowish-white to light orange fine crystalline powder. It is a weak acid that, in solutions, can lose H+ ions.
How to prepare phenolphthalein indicator for titration:
- Weigh accurately 01.00 gm of phenolphthalein 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 ethanol.
- The concentration of the prepared solution is about 10 g/L.
Phenolphthalein has a pKa of 9.7 and the pH range is 8.2 to 10. It is colorless in acidic solutions, while in a basic condition it turns pink. In acid-base titration, is frequently used as an indicator.
References:
- Wikipedia contributors. (2022, January 23). Phenolphthalein. 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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