Which Is the Best Colored Indicator to Use in the Titration

question 13

Multiple Choice

Which is the best colored indicator to use in the titration of 0.1 M CH₃CO₂H(aq) with NaOH(aq) ? Why? (K_a of CH₃CO₂H = 1.8 × 10^-5, K_b of CH₃CO₂^- = 5.6 × 10^-10) $$\begin{array} { l l } \text { Indicator } & \mathrm { p } K _ { \mathrm { a } } \\\hline \text { Bromcresol Green } & 4.8 \\\text { Bromthymol Blue } & 6.8 \\\text { Phenolphthalein } & 9.2\end{array}$$

• A) Bromcresol Green. The equivalence point for a weak acid titration occurs at low pH.
• B) Bromthymol Blue. The pH at the equivalence point is 7.0.
• C) Bromcresol Green. The pK_a of CH₃CO₂H and the pK_a of the indicator are similar.
• D) Phenolphthalein. The pK_a of CH₃CO₂^- and the pK_b of the indicator are similar.
• E) Phenolphthalein. The pH at the equivalence point is near the pK_a of the indicator.

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