Phenolphthalein is colorless in its protonated form and pink in its deprotonated…
CHEMISTRY · Single correct · A Level · Chemistry · Acids and bases · Acids and bases
Problem
Phenolphthalein is colorless in its protonated form and pink in its deprotonated form; it has a pKa of 9.3. A solution remains colorless after the indicator is added. Which statement about the solution is most consistent with this observation?
(a) The pH is greater than 9.3 because the deprotonated form dominates.
(b) The pH is less than 9.3 because the protonated form dominates.
(c) The pH is approximately 9.3 because both forms are present in equal amounts.
(d) The pH is less than 8.2, well below 9.3, because the indicator is colorless only when fully protonated.