Which of the following is true for weak acid + strong base titration?

Question

BlackTom AI · Accepted Answer

Question restatement: You are titrating a weak acid with a strong base and asked which statement is true.

Option: 'Buffer solution forms before equivalence'

Reasoning for this option: In a titration where a weak acid (HA) is titrated with a strong base (OH-), initial solution contains HA. As base is added, HA is progressively neutralized to form its conjugate base A- and water: HA + OH- -> A- + H2O. During the portion of the titration before the equivalence point, both HA and its conjugate base A- coexist in the solution in appreciable amounts, creating a buffer system. This is precisely the condition described by the Henderson–Hasselbalch relationship, which governs buffer behavior when there is a mixture of a weak acid and its conjugate base.

Why this makes sense: A buffer is effective when there is a significant ratio of weak acid to conjugate base. Here, prior to complete neutralization, the solution contains both species in varying proportions, yielding buffering capacity around the pH that is not strongly acidic or basic. The buffer region is characteristic of weak acid–strong base titrations and is observed on the titration curve as a relatively flat region.

Why this statement could be misunderstood: If one expects only a strong buffer throughout the titration, that would be incorrect because once nearly all HA is converted, the solution becomes dominated by A- and OH-, and the buffering capacity changes; after equivalence, the pH rises more steeply due to excess OH-. However, the specific claim that a buffer forms before the equivalence point is consistent with the standard interpretation of weak acid–strong base titrations.

Note on completeness: In a multiple-choice setting about this titration, other statements might address the pH at the equivalence point (which is >7 for a weak acid–strong base titration) or the shape of the titration curve, but since only this option is provided, the reasoning supports its truth in the context of the typical titration behavior.

CHM-1020-LD01.2025SU Exam 2

Which of the following is true for weak acid + strong base titration?

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