Learn the procedure for making cresol red 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.
Cresol red (C21H18O5S) chemically described as o-cresolsulphonphthalein is a triarylmethane dye used as a pH indicator. It comes in dark green or brown-red powder or crystals which is sparingly soluble in water and soluble in ethanol.
How to prepare cresol red indicator for titration:
- Weigh accurately 20 mg of cresol red and pour it into a 100.00 ml volumetric flask containing 01.06 ml of 0.05N sodium hydroxide solution and 05.00 ml of 95% ethanol.
- Once it is dissolved, add 15 ml of ethanol and dilute to 100.00 ml with distilled water.
- The concentration of the prepared solution is about 0.2 g/L.
Cresol red has a pKa of 1.0 and pH ranges of 0.2-1.8 and 7.2 to 8.2. At pH 0.2-1.8, it changes from red to yellow, while at pH 7.2 to 8.2, it transitions from yellow to violet-red. It is frequently used as an indicator in acid-base titration.
References:
- Wikipedia contributors. (2021, May 8). Cresol 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.
You may also like this:
No comments:
Post a Comment