Question

Which of the following indicator is most suitable for titration of $HB$ with strong base

• A. $\text{Phenolphthalein}(8.3-10)$
• B. $\text{Bromothymol}(6-7.6)$
• C. $\text{Methyl red}(4.2-6.3)$
• D. $\text{Malachite Green}(11.4-13)$

Answer 1

The correct option is A $\text{Phenolphthalein}(8.3-10)$

Concept :-

Indicators are pH sensitive compounds which ionized at different pH values. Ionization alters the shape and charge of indicator molecules therefore their color changes at different pH values.

Phenolphthalein ionized at pH range $8.3$ to $10$ and become pink in color but as the pH increases above $10$, its binds with titrating compound to form a complex and turns into purple above pH $10$.

$H{I}_n+H_{2}O\rightleftharpoons \underset{Pink}{I{n}^{-}}+H_3{O}^{+}$
Option A is the correct answer