A 25.0-mL sample of 0.150 M benzoic acid is titrated with a 0.150 M NaOH solution.What is the pH before any base is added? The K_a of benzoic acid is 6.3 × 10^-5. A) 4.19 B) 6.5 × 10^-5 C) 4.20 D) 3.38 E) 2.4 × 10³

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The pH before any base is added can be calculated using the Henderson-Hasselbalch equation:pH = pKa + log([A-]/[HA])where pKa is the negative logarithm of the acid dissociation constant, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the acid.In this case, the pKa of benzoic acid is 6.3 × 10-5, and the initial concentration of benzoic acid is 0.150 M. Since no base has been added yet, the concentration of the conjugate base is 0 M. Therefore, the pH before any base is added is:pH = 6.3 × 10-5 + log(0/0.150) = 4.19

A 250-ML Sample of 0