Juglone and Lawsone as Acid-Base Indicators

Abstract

Juglone and lawsone, both acid-base indicators, obtained from natural sources and give pink and red colours with aqueous alkalies, respectively. Their transition ranges are found to be pH 7.4-8.2 and 2.6-3.4. To establish the transition intervals, a buffer series ranging in the pH values from 2.0-2.2-2.4-2.6-2.8-3.0-3.2-3.4-3.6-3.8-4.0-4.2-4.4-4.6-4.8-5.0-5.2-5.4-5.6-5.8-6.0-6.2-6.4-6.6-6.8-7.0-7.2-7.4-7.6-7.8-8.0-8.2-8.4-8.6-8.8-9.0 has been used. Juglone can be used for the titrations of strong acids with strong bases and weak acids with strong bases and lawsone can be used for the titration of strong acids with weak bases only. Permanancy of the colours at the end point is one of their advantages. © 1977, Walter de Gruyter. All rights reserved.