Between the pH range of 8.0 - 9.6 s.u., what color change does phenolphthalein undergo with increasing pH?

Phenolphthalein is a common pH indicator used in titrations that exhibits a distinct color change in response to pH levels. In acidic environments (pH below 8.2), phenolphthalein is colorless. As the pH increases and surpasses this threshold, the solution transitions to a pink or red color, indicating that the solution is becoming more basic. This color shift occurs due to the ionization of phenolphthalein; at a pH of around 8.2 to 9.6, the molecule loses protons, leading to the formation of its conjugate base, which is responsible for the pink hue observed.

In the context of the specified pH range of 8.0 - 9.6 s.u., the relevant color change is from colorless (at lower pH) to pink or red (at higher pH). Thus, the correct choice reflects this transformation, confirming that the phenolphthalein indicator exhibits a noticeable color change that signals a move towards a more alkaline condition. Understanding this behavior is vital for accurately interpreting pH levels in various water quality assessments.