🧪 Topic Summary
Weak base-strong acid titrations involve the reaction of a weak base with a strong acid. Unlike strong acid-strong base titrations, the pH at the equivalence point is not 7. This is because the conjugate acid of the weak base affects the pH. The titration curve shows a gradual decrease in pH until the equivalence point, followed by a more rapid decrease as excess strong acid is added. Understanding the $K_b$ of the weak base and the stoichiometry of the reaction is crucial for calculating pH at various points along the curve.
The key to solving these problems is to break the titration into stages: before any acid is added, before the equivalence point, at the equivalence point, and after the equivalence point. Each stage requires different calculations involving equilibrium constants and stoichiometry.
🧠 Part A: Vocabulary
Match the term with its correct definition:
| Term |
Definition |
| 1. Equivalence Point |
A. The point where the moles of acid equal the moles of base. |
| 2. Buffer Solution |
B. A solution that resists changes in pH. |
| 3. $pK_b$ |
C. $-log(K_b)$, where $K_b$ is the base dissociation constant. |
| 4. Titration Curve |
D. A plot of pH versus the volume of titrant added. |
| 5. Conjugate Acid |
E. The species formed when a base accepts a proton. |
✍️ Part B: Fill in the Blanks
A weak base-strong acid titration involves the reaction of a ______ base with a ______ acid. The pH at the equivalence point is ______ 7 due to the formation of the conjugate ______. The titration curve shows a gradual ______ in pH as the strong acid is added.
🤔 Part C: Critical Thinking
Explain how the $K_b$ value of a weak base affects the shape of its titration curve when titrated with a strong acid. How does a smaller $K_b$ value change the curve, and why?