Which indicator is commonly used to determine neutralization end-points in acid-base titrations?

• A. Methyl orange
• B. Bromothymol blue
• C. Litmus
• D. Phenolphthalein

Answer: (D)

Choosing the right indicator depends on where the neutralization point falls on the pH scale. You want the indicator to change color right as the acid and base have neutralized each other, so the endpoint matches the equivalence point.

Phenolphthalein is ideal because it stays colorless in acidic solutions and turns pink as the solution becomes basic, with a color-change range around pH 8.2 to 10. This places the endpoint in the typical region reached at the equivalence point for many acid–base titrations, especially when the base is added to an acid. That sharp color shift gives a clear, easy-to-see endpoint.

Other indicators have color-change ranges that don’t align as well with the end point of many titrations. Methyl orange changes in the acidic range, so it can signal the endpoint too early. Bromothymol blue and litmus either change near neutral but with less distinct color transitions or broader ranges, making the endpoint harder to pinpoint precisely.