Learn the procedure for making methyl red indicator solution.
The compounds that change color when exposed to acidic or basic solutions are called indicators. 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 methyl red indicator for titration:
- Weigh accurately 50.00 mg of methyl red and pour it into a 100.00 ml volumetric flask containing 01.86 ml of 0.1 M sodium hydroxide solution and 05.00 ml of 95% ethanol, warm it.
- After the solution has been effected, add 45.00 ml of 95% ethanol and dilute to 100.00 ml with distilled water.
- The concentration of the prepared solution is about 0.5 g/L.
Methyl red (C15H15N3O2), commonly known as C.I. Acid Red 2, is a pH indicator that comes in a dark red crystalline powder. It can be prepared by diazotizing anthranilic acid and then reacting it with dimethylaniline.
It has a pKa of 5.0 and the pH range is 4.2 to 6.2. In an acidic medium (less than 4.4), methyl red turns red, while in a basic condition (higher than 6.2), it turns yellow, and shows orange color in between, with a pKa of 5.1.
Methyl red can be used as an indicator in acid-base titrations involving the strong base and weak acid. It is also used as a dye for the food, leather, and textile industries.
References:
- Wikipedia contributors. (2021, November 19). Methyl 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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