Which of the following are common indicators used in acid-base titrations?

The choice of phenolphthalein and bromothymol blue as common indicators in acid-base titrations is appropriate due to their distinct color changes at specific pH levels, which help in identifying the endpoint of a titration effectively.

Phenolphthalein is colorless in acidic solutions and turns pink in alkaline solutions, making it particularly useful for titrations involving strong acids and strong bases where a noticeable transition occurs around pH 7 to 8.2. This clear visual cue allows for accurate determination of when the reaction has reached its equivalence point.

Bromothymol blue, on the other hand, transitions from yellow in acidic conditions (below pH 6) to blue in alkaline solutions (above pH 7.6). This indicator is useful in titrations involving weak acids and strong bases, where the pH change around the endpoint can sharply contrast with the starting reactants.

Both of these indicators provide reliable and distinct color changes that are easy to observe, which is key in ensuring precision during titrations. Their application is well-known among chemists, making them standard choices in laboratory practices involving acid-base reactions.