A compound 'X' is a weak acid and it exhibits colour change at pH close to the equivalence point during neutralization of NaOH with $\mathrm{CH}_{3}\mathrm{COOH}$. Compound 'X' exists in ionized form in basic medium. The compound 'X' is :

JEE Main · 2022 · 29 Jul 2022 · Shift 2 · Equilibrium

A compound 'X' is a weak acid and it exhibits colour change at pH close to the equivalence point during neutralization of NaOH with

CH_{3} COOH

. Compound 'X' exists in ionized form in basic medium. The compound 'X' is :

(A)methyl orange
(B)methyl red
(C)phenolphthalein✓ Correct
(D)erichrome Black T

Answer: (C)

Solution

The neutralization of

CH X_{3} COOH

(weak acid) with

NaOH

(strong base) gives a basic equivalence point (pH ≈ 8-9). Phenolphthalein is a weak acid indicator that changes color in the pH range 8.3-10.0 (colorless in acidic/neutral, pink in basic medium), making it suitable for this titration. It exists in ionized form in basic medium. Methyl orange and methyl red have lower pH transition ranges and are not suitable for weak acid-strong base titrations.

JEE Main · 2022 · 29 Jul 2022 · Shift 2 · Single correct option

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