Final answer:
A pH indicator such as Universal Indicator is commonly used for general pH testing, whereas phenolphthalein can be chosen for reactions with a basic equivalence point. The pKin of the indicator is essential for clear and rapid color changes at the desired pH.
Step-by-step explanation:
The name of the pH indicator used for colorimetric method varies depending on the specific pH range of interest and the reaction being monitored. For a general pH screening, Universal Indicator would be appropriate as it covers a wide range of pH values and displays multiple colors that correspond to different pH levels. Alternatively, indicators such as phenolphthalein can be used for reactions expected to have an endpoint in the basic range, as it changes from colorless to pink at around pH 8.3, indicating a more basic solution.
When selecting a pH indicator, it is crucial to consider the transition range and to ensure that the indicator’s pKin is within one pH unit of the expected pH at the equivalence point of the titration. This ensures an easily detected and rapid color change without the indicator reacting with the substance being titrated.