Learn the procedure for making a catechol violet indicator solution.
The compound that changes color when exposed to acidic or basic solutions is called an indicator. Color indicators are commonly used to measure pH and are added to the reaction mixture to identify the titration endpoint/equivalence point.
Catechol violet (C19H14O7S) is an azo dye used in complexometric titrations as an indicator. This phthalene dye chelates metals to form blue to blue-violet complexes. When alkaline, it is known to be unstable. At a neutral pH, the stability improves. The color can be yellow when the pH is between 2 and 7.
It comes in dark-red-brown metallic or crystalline powder which is soluble in water, ethylene glycol, monomethyl ether, and ethanol.
How to prepare catechol violet indicator for titration:
- Weigh accurately 0.1 gm of catechol violet and pour it into a 100.00 ml volumetric flask containing 50.00 ml of distilled water and swirl until it completely dissolved.
- Once it is dissolved, dilute to 100.00 ml with distilled water.
- The concentration of the prepared solution is about 01 gram/liter.
Pyrocatechol violet has pKa values of 7.21. Its pH range is 0.0 to 8.0. It is used as a metal indicator and turns from red to violet over the pH range.
References:
- Wikipedia contributors. (2022, January 21). Catechol. 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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