What are common indicators used in acid-base titrations?

In acid-base titrations, indicators are substances that change color at a certain pH, helping you determine the endpoint of the titration. Common indicators include:

1. Phenolphthalein
   • Colorless in acidic solution.
   • Turns pink in basic solution (around pH 8.2–10).
   • Used for strong acid vs. strong base or strong acid vs. weak base titrations.
2. Methyl Orange
   • Red in acidic solution.
   • Turns yellow in basic solution (around pH 3.1–4.4).
   • Used for strong acid vs. strong base or strong acid vs. weak base titrations.
3. Methyl Red
   • Red in acidic solution.
   • Turns yellow in basic solution (around pH 4.4–6.2).
   • Used for strong acid vs. weak base titrations.
4. Bromothymol Blue
   • Yellow in acidic solution.
   • Blue in basic solution (around pH 6.0–7.6).
   • Suitable for strong acid vs. strong base titrations.
5. Thymol Blue
   • Has two color change ranges:
     • pH 1.2–2.8 (red to yellow)
     • pH 8.0–9.6 (yellow to blue)
   • Used depending on the type of acid-base titration.

Summary Tip: The choice of indicator depends on the type of acids and bases involved and the expected pH at the equivalence point.