Question

The indicator(s) appropriate for the determination of end point in the titration of a weak acid with a strong base is/are

• A. phenolphthalein
• B. thymol blue
• C. bromophenol blue
• D. methyl orange

Hint:

Always match the indicator pH range with the pH at equivalence point of the titration.

Answer 1

The Correct Option is A, B

Step 1: Understanding the titration type.
A weak acid–strong base titration has an equivalence point in the basic range (pH ≈ 8–10). Therefore, the indicator must change color in the basic region.
Step 2: Analyzing the indicators.
(A) Phenolphthalein: pH range 8.3–10 → suitable → correct.
(B) Thymol blue (first range acidic) → not suitable.
(C) Bromophenol blue (pH 3–4.6) → unsuitable.
(D) Methyl orange (pH 3.1–4.4) → unsuitable for basic equivalence point.
Step 3: Conclusion.
Phenolphthalein is the correct indicator for weak acid–strong base titrations.