Consider the titration curves (labeled a and b) for two weak bases, both titrated with 0.100 M HCl. (a)



(b)

(ii) Which base has the larger Kb?

Verified step by step guidance

1. Identify the initial pH of both titration curves. The initial pH is higher for the base with the larger Kb.
2. Observe the shape of the titration curves. The curve with a more gradual slope before the equivalence point indicates a weaker base.
3. Determine the volume of HCl added at the equivalence point for both curves. The equivalence point occurs where the pH drops sharply.
4. Compare the pH at the equivalence point for both curves. The base with the higher pH at the equivalence point has a larger Kb.
5. Conclude which base has the larger Kb by comparing the initial pH and the pH at the equivalence point for both titration curves.

Key Concepts

Titration Curves

Titration curves graphically represent the change in pH of a solution as a titrant is added. In this case, the weak bases are being titrated with a strong acid (HCl), leading to a characteristic S-shaped curve. The steepest part of the curve indicates the equivalence point, where the amount of acid equals the amount of base present, and the pH changes rapidly.

Weak Base and Kb

Weak bases partially dissociate in solution, establishing an equilibrium between the base and its conjugate acid. The base dissociation constant (Kb) quantifies this equilibrium, with larger Kb values indicating a stronger weak base that dissociates more in solution. Comparing the titration curves can help determine which base has a larger Kb based on the steepness and position of the pH change.

Equivalence Point

The equivalence point in a titration is reached when the amount of titrant added is stoichiometrically equivalent to the amount of substance being titrated. For weak bases titrated with a strong acid, this point is characterized by a significant drop in pH. Analyzing the pH at the equivalence point can provide insights into the strength of the base and its Kb value.