What color does phenolphthalein show in alkaline solutions?

Phenolphthalein is a common pH indicator that is used to determine the acidity or alkalinity of a solution. In alkaline solutions, phenolphthalein exhibits a distinct pink color. This color change occurs because, in the presence of a basic or alkaline substance, the structure of the phenolphthalein molecule changes, leading to the formation of a colored ion.

When the pH of the solution increases beyond approximately pH 8.2, phenolphthalein transitions from a colorless form to its ionized, colored form, which is pink. This property makes it a useful indicator in titrations involving strong bases, where it can visually signal the endpoint of the reaction by changing color from colorless to pink as the solution shifts to a more alkaline state.

In contrast, in acidic environments (lower pH levels), phenolphthalein remains colorless, clearly indicating that it is not in an alkaline condition. Therefore, the pink coloration in alkaline solutions is a key feature of phenolphthalein and confirms its function as a reliable pH indicator.