A student titrates 25.00 mL of 0.100 M acetic acid with 0.100 M NaOH while monitoring pH. Selected pH values: at 0.00 mL added, pH = 2.87; at 12.50 mL (half-equivalence), pH = 4.74; at 25.00 mL (equivalence), pH = 8.72.
Which indicator is most suitable for finding the equivalence point?
- A
Bromocresol green (range 3.8-5.4)
- B
Methyl red (range 4.4-6.2)
- C
Methyl orange (range 3.1-4.4)
- Dcheck_circle
Phenolphthalein (range 8.2-10.0)
Explanation
Equivalence pH = 8.72 (basic because acetate is conjugate base of weak acid). Phenolphthalein's range covers this; the other indicators change color far before equivalence.