Acid-base titration setup: The pink color is caused by the phenolphthalein indicator.
Before you begin the titration, you must choose a suitable pH indicator, preferably one that will experience a color change (known as the “end point”) close to the reaction’s equivalence point; this is the point at which equivalent amounts of the reactants and products have reacted. Below are some common equivalence point indicators:
- strong acid – strong base titration: phenolphthalein indicator
- weak acid – weak base titration: bromthymol blue indicator
- strong acid-weak base titration: methyl orange indicator the base is off the scale (e.g., pH > 13.5) and the acid has pH > 5.5: alizarine yellow indicator
- the base is off the scale (e.g., pH > 13.5) and the acid has pH > 5.5: alizarine yellow indicator
- the base is off the scale (e.g., pH > 13.5) and the acid has pH > 5.5: alizarine yellow indicator
- the acid is off the scale (e.g., pH < 0.5) and the base has pH < 8.5: thymol blue indicator