Final answer:
The student's question pertains to the use of phenolphthalein as an acid-base indicator in alkaline solutions, where it turns pink. This indicates a pH greater than 8.3.
Step-by-step explanation:
The use of acid-base indicators such as phenolphthalein is a way to determine the pH of a solution in chemistry. These indicators change color at specific hydronium ion concentrations. Phenolphthalein, for instance, turns pink in alkaline solutions with a pH greater than 8.3, where the hydronium ion concentration is less than 5.0 × 10⁻⁹ M.
Alkaline solutions also turn red litmus paper blue, which is another method to indicate a high pH (greater than 7). It is important to note that adding substances such as alum, which was historically used to make bread look whiter, would not be appropriate for adjusting the pH of solutions for such tests.