Learn the procedure for making methyl orange 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 orange indicator for titration:
- Weigh accurately 0.1 g of methyl orange and dissolve in 50 ml of 95% ethanol in a volumetric flask, and properly mix it. Once it has completely dissolved, make up the volume up to 100 ml with ethanol.
- The concentration of the prepared solution is about 1 g/L.
Methyl orange (C14H14N3NaO3S) is an organic compound that an azo dye prepared from sulfanilic acid and N,N-dimethylaniline. It has a pKa of 4.2 and the pH range is 3.1 to 4.4.
In an acidic medium, methyl orange turns red, while in a basic condition, it turns yellow and in neutral solution it shows orange colour. It's commonly used in acid titration since it changes color at the pKa of a mid-strength acid.
Methyl orange, unlike a universal indicator, does not have a wide range of color changes, however has a sharp end point.
References:
- Wikipedia contributors. (2021, September 27). Methyl orange. 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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