The indicator phenolphthalein changes colour at pH ~ 9. This indicator is NOT suitable for accurate… · ABC26IN0543
Subject: Inorganic Chemistry · Chapter: Analytical Chemistry · Topic: Analytical Chemistry & Instrumental – General · Exam: JAM 2005-2022 · Marks: 2 · Difficulty: Medium
The indicator phenolphthalein changes colour at $\mathrm{pH} \sim 9$. This indicator is NOT suitable for accurate determination of the end point in the titration of
(a)$\mathrm{CH}_{3} \mathrm{COOH}$ with NaOH
(b)HCl with $\mathrm{NH}_{4} \mathrm{OH}$
(c)HCl with NaOH
(d)HCl with KOH
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
HCl vs NH₄OH (weak base) has its equivalence point near pH 5; phenolphthalein changes at pH ≈ 9 and would give a late, indistinct end point. The other three titrations pass through pH 9 at the steep part of the curve.