When choosing an indicator for an acid-base titration, one must consider the following:

1. One factor to consider is thepH range. Choose an indicator with a pH range that falls within the pH of the specific reaction. For example, during the titration of a strong acid with a strong base, the pH rapidly changes from 3 to 11. Thus, a good indicator for that reaction is phenolphthalein (whose range spans from pH 8-10). Another factor is color change. 
2. A good indicator must have a clear and distinct color changethat is easily recognizable. The color change should also be sharp and occur over a narrow pH range. A third factor is the indicator’s chemical stability. 
3. An ideal indicator should bechemically stableand not react with either the acid or the base. If an indicator reacts with either one, it may alter the accuracy of the titration. 
4. Additional factors include the availability and costs, as some indicators are more commercially available and less expensive than others. 
5. Lastly, the indicator should be sensitive to small changes in pH. This is vital for the titration because the endpoint of the reaction is typically very close to the equivalence point. If the indicator is not sensitive enough, it may not show a distinct color change at the endpoint.