Question

what feature is present on a weak acid titration curve but not on a strong acid titration curve?
buffer region
steep ph shift
equivalence point
excess strong base
question 4
in the case of a weak acid titration, what occurs in the buffer region?
the ph undergoes a rapid change.
the ph remains relatively constant.
the ph is not equal to the pka of the weak acid.
the ph is neutral.

Explanation:

• For the first question:
• A buffer region is present in a weak - acid titration curve. In a weak - acid titration, before reaching the equivalence point, a significant amount of the weak acid and its conjugate base (formed by the reaction with the titrant, usually a strong base) co - exist. This forms a buffer system. In a strong - acid titration, since the strong acid is completely dissociated, there is no such co - existence of a weak acid and its conjugate base in significant amounts to form a buffer region.
• Both strong and weak acid titration curves have a steep pH shift (at the equivalence point), an equivalence point (where the amount of titrant is stoichiometrically equal to the amount of acid), and a region of excess strong base (after the equivalence point when more base is added).
• For the second question:
• In the buffer region of a weak - acid titration, according to the Henderson - Hasselbalch equation \(pH = pK_a+\log\frac{[A^ - ]}{[HA]}\). When small amounts of acid or base (in the context of the titration, small additions of the titrant base) are added in the buffer region (where \([HA]\) and \([A^-]\) are both in significant amounts), the ratio \(\frac{[A^ - ]}{[HA]}\) changes only slightly. So, the pH remains relatively constant.
• The pH undergoes a rapid change at the equivalence point (not in the buffer region). At the half - equivalence point (a point within the buffer region), \(pH = pK_a\). And the pH is neutral (\(pH = 7\)) only for the titration of a strong acid with a strong base at the equivalence point, while for a weak - acid - strong - base titration, the pH at the equivalence point is basic (\(pH>7\)) and in the buffer region, it is not neutral.

Answer:

Buffer region
The pH remains relatively constant.