Question

Phenolphthalein, Kₐ =7.0×10⁻¹⁰ , is colorless in its protonated form (HX) and fuchsia in its ionized form ( X ). At what pH will phenolphthalein be a pink color? Express your answer to one decimal place.

Answer 1

Phenolphthalein will exhibit a pink color in a solution when the pH is above 8.3, as it transitions from colorless to pink at this pH level.

Step-by-step explanation:

Phenolphthalein will exhibit a pink color in a solution when the pH is above 8.3, as it transitions from colorless to pink at this pH level. Phenolphthalein is a chemical compound used as an acid-base indicator that exhibits a color change within a certain pH range. Specifically, it changes from colorless to fuchsia or pink. The indicator is colorless below a pH of about 8.3 and transitions to pink at higher pH levels, thus informing us about the solution's acidity or basicity.

According to provided information, phenolphthalein has a Ka of 7.0×10⁻¹⁰ and will turn pink in a solution where the hydronium ion concentration is less than 5.0×10⁻⁹ M, which corresponds to a pH greater than 8.3. Therefore, it can be concluded that phenolphthalein will exhibit a pink color in solutions where the pH is above 8.3.