Learn the procedure for making bromophenol 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.
Bromophenol blue (C19H10Br4O5S) chemically described as 3, 5, 3’, 5’-tetrabromophenolsulphonphthalein, is a dye used as a pH indicator. It is prepared by adding slowly excess bromine to a heated phenolsulfonphthalein solution in glacial acetic acid. Bromophenol blue has a similar structure to phenolphthalein. It comes as a pink-orange to red to purple powder, generally used as a fluorescent stain in yeast cells.
How to prepare bromophenol blue indicator for titration:
- Weigh accurately 40 mg of bromophenol blue and pour it into a 100.00 ml volumetric flask containing 01.20 ml of 0.05N sodium hydroxide solution and 10.00 ml of 95% ethanol, warm it.
- Once it is dissolved, dilute to 100.00 ml with distilled water.
- The concentration of the prepared solution is about 0.4 g/L.
Bromophenol blue has a pKa of 4.0 and the pH range is 3.5 to 4.6. It is turn yellow below pH 3.5, while it turns blue above pH 4.6, this reaction is reversible. It is mainly used as an acid-base indicator, also used as a dye.
References:
- Wikipedia contributors. (2022, January 25). Bromophenol 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:
- Sabnis, R. W. (2008). Handbook of Acid-Base Indicators. Boca Raton, FL: CRC Press.
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