At what pH level is phenolphthalein alkalinity determined?

Phenolphthalein alkalinity is specifically determined at a pH level of 8.3. At this pH, phenolphthalein changes color from colorless to pink, indicating the presence of alkaline substances in the water sample being tested. This transition occurs because phenolphthalein acts as a pH indicator, specifically denoting the endpoint of a titration where the pH is slightly above the neutral level, showing that the sample has sufficient hydroxide ions likely due to the presence of weak acids or basic metals, such as carbonates or hydroxides.

The choice of pH 8.3 is significant in water quality analysis, as it provides a clear visual representation that quantifies the alkaline content in a sample. This tested alkalinity is imperative in assessing the water's buffering capacity, which impacts its ability to handle pH changes caused by various pollutants or processes. Hence, the determination of alkalinity at this specific pH level is crucial in water quality management and treatment processes.