Three 25.00-mL samples of approximately 0.10 M phenol, \(\ce{C6H5OH}\), Ka = 1.0 × 10-10 were removed from a container and placed in separate 250-mL beakers. The samples were titrated with standard potassium hydroxide, KOH, solution. Cresol red was the acid–base indicator used in the titration. The samples required 31.75, 32.38, and 41.75 mL to reach the endpoint. Which of the following might explain why one of the samples required significantly greater amount of base to reach the endpoint?

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