Acid-base titration is a technique in which precise volumes of a titrant (an acid or base solution) are added incrementally to a known volume of a sample solution (a base or acid solution, respectively). In acid-base titration experiments, equivalence points are reached when the amounts of base and acid in the solution are chemically equivalent. On acid-base titration graphs, equivalence points are characterized by a relatively large change in pH over a relatively small change in titrant volume. Two titration experiments were performed at 25oC. In both experiments, a 0.10 M sodium hydroxide (NaOH) solution was used to titrate an acidic solution. All solutions were aqueous. Experiment 1 A 0.10 M NaOH solution was slowly added to 200 mL of a 0.01 M hydrochloric acid (HCl) solution. After each addition of NaOH, the solution was stirred and the pH measured using a pH meter and recorded. See Figure 1. Experiment 2 Experiment 1 was repeated, except 0.10 M NaOH was added to 25 mL of an unknown acidic solution. The titration curve is displayed in Figure 2. Acid-base indicators are substances which change colors over certain pH ranges. The colors of four acid-base indicators over a range of pH values are shown in the table below (B = blue, G = green, P = purple, O = orange, R = red, Y = yellow). ScienceTable A student wants to use an acid-base indicator to identify the equivalence point from Experiment 1. Which of the following indicators should she use? Methyl Yellow Bromophenol Blue Methyl Purple Phenol Red