Question

What are the alkali indicators? According to Quinonoid theories, explain their methodology.

Answer 1

Alkali indicator are substances that have different color variations in acidic and alkaline solution. In other words, acid-alkali indicator is weak acid or weak alkaline. Hydrogen ion $\bf [H {}^{ + } ]$ concentration or hydroxide ion $\bf [OH {}^{ - } ]$ concentration in this solution, ie, change the color of the pH value by changing its color.



According to the principle of quinoneoid, acid-alkaline indicator is present in two transient forms, which differ in structures. Both . Trivial forms reside in each other with each other. The color of both forms of the indicators is colorless or light colored and darker, respectively.




The form of light colored bengineoid structure and dark color is called quinoneoid structure. In acidic and alkaline medium, one of the two forms is mainly acidic and the second is mainly present in the alkaline medium. When the pH of the medium changes, the variable is converted into one form and it changes the color of the solution.