Which statement is correct concerning the resulting titration curve when a weak acid is titrated with a strong base?

• A. The initial pH is determined by the concentration of the strong base.
• B. The pH at the equivalence point is greater than 7.
• C. The pH after the equivalence point is determined using the K_a of the weak acid.
• D. The pH at the equivalence point is equal to 7.

Answer: (B)

Verified step by step guidance

1. Understand the nature of the titration: In a titration involving a weak acid and a strong base, the weak acid will react with the strong base to form water and a conjugate base. This reaction affects the pH at various points in the titration curve.
2. Identify the initial pH: The initial pH of the solution is determined by the weak acid itself, not the strong base. Since weak acids partially dissociate, the initial pH will be less than 7 but greater than the pH of a strong acid of the same concentration.
3. Determine the pH at the equivalence point: At the equivalence point, all the weak acid has been converted to its conjugate base. The pH at this point is determined by the hydrolysis of the conjugate base, which typically results in a pH greater than 7. This is because the conjugate base can react with water to form OH⁻ ions, making the solution basic.
4. Consider the pH after the equivalence point: After the equivalence point, the pH is determined by the excess strong base added. The concentration of the strong base will dictate the pH, which will be greater than 7.
5. Clarify the incorrect statements: The initial pH is not determined by the strong base, and the pH at the equivalence point is not equal to 7. The pH after the equivalence point is not determined using the K_a of the weak acid, but rather by the excess strong base.