Final answer:
In a titration curve for a weak acid titrated with a strong base, the buffer region appears as a nearly flat line around the midpoint, where the pH changes little with the addition of the strong base. This shows the formation of a buffer and occurs roughly from one pH unit below to one pH unit above the pKa of the weak acid involved.
Step-by-step explanation:
In the context of titration curves, the buffer region is a section of the curve where the pH changes minimally with the addition of titrant. This specific region occurs around the midpoint of the titration of a weak acid with a strong base, symbolizing when about half of the weak acid has been neutralized. The buffer region is characterized by a nearly horizontal line in the titration curve, reflecting the presence of a buffer that resists changes in pH. This region extends approximately from a pH value of 1 unit less than the pKa to a pH value of 1 unit greater than the pKa, illustrating the optimal buffering capacity at a pH close to the pKa of the acid in the buffer solution.
Demonstrated in a schematic titration curve, the acid-base properties of the solution are governed by the equilibrium for dissociation of the weak acid before the midpoint, and by the equilibrium for reaction with water of the conjugate base formed after the midpoint. This results in a distinct, nearly flat portion around pKa, indicating the buffer's effectiveness. Hence, during the titration of a weak acid or a weak base, the shape of the titration curve and the pH change around the equivalence point rely heavily on the identity of the substance and its dissociation constant (Ka or Kb).