In an acid–base titration, what is the primary purpose of adding an indicator?

• A. To increase the reaction rate so the titration reaches completion faster
• B. To produce a visible change (e.g., color change) near the equivalence point that signals the end point has been reached
• C. To prevent dilution effects by buffering the solution throughout the titration
• D. To ensure the titrant concentration remains constant during the titration

Answer: (B)

Verified step by step guidance

1. Understand that an acid-base titration involves gradually adding a titrant to a solution until the amount of titrant neutralizes the analyte, reaching the equivalence point.
2. Recognize that the equivalence point is the theoretical point where the moles of acid equal the moles of base, but it is not always easy to detect directly.
3. Learn that an indicator is a chemical substance that changes color at a specific pH range, which is chosen to be close to the equivalence point of the titration.
4. Know that the primary purpose of adding an indicator is to produce a visible change, such as a color change, near the equivalence point to signal the end point of the titration.
5. Distinguish this purpose from other options: indicators do not increase reaction rate, prevent dilution, or maintain titrant concentration; their role is purely to provide a visual cue.