Which of the following indicators would be the best to use when 0.050 M benzoic acid (K_a = 6.6 × 10⁻⁵) is titrated with 0.05 MNaOH? A)Bromphenol blue, pH range: 3.0-4.5 B)Bromcresol green, pH range: 3.8-5.4 C)Alizarin, pH range: 5.7-7.2 D)Phenol red, pH range: 6.9-8.2 E)Phenolphthalein, pH range: 8.0-10.1

Question

Quizplus · Accepted Answer

Since benzoic acid has a pKa value of 4.20, it will be best to choose an indicator with a pH range within 1 pH unit of its pKa value, which is Phenol red in this case (pH range: 6.9-8.2). Phenol red changes color at a pH range that overlaps with the benzoic acid's pH range, making it the best choice for this titration.

Which of the Following Indicators Would Be the Best to Use