A student performs a titration of a \(25.0 \text{ mL}\) sample of \(0.10 \text{ M } \text{CH}_3\text{COOH(aq)}\) (\(K_a = 1.8 \times 10^{-5}\)) with \(0.10 \text{ M } \text{NaOH(aq)}\). The student must select an appropriate acid-base indicator from a laboratory chart that lists the \(pK_a\) and color-transition range for several candidate indicators. Which of the following pieces of information provides the most direct evidence needed to select the indicator that will change color closest to the stoichiometric equivalence point?