Question detail
What is the shape of the pH curve when a strong acid is titrated with a strong base?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Acids and bases (A-level only)
Question
- A. A steep rise at the equivalence point followed by a plateau
- B. A gradual slope throughout the titration
- C. A flat line with no change in pH
- D. A steep decline followed by a gradual increase
Answer
A steep rise at the equivalence point followed by a plateau
Explanation
The pH curve for a strong acid titrated with a strong base shows a steep rise at the equivalence point due to the rapid neutralization of the acid by the base, resulting in a significant change in pH over a small volume of added base.
Common mistake
Misunderstanding pH Curve Shapes
Students often incorrectly assume that the pH curve for a weak acid-strong base titration will have a steep slope throughout the entire range, similar to that of a strong acid-strong base titration.
To correct this, remember that the pH curve for a weak acid-strong base titration will show a more gradual slope before the equivalence point due to the weak acid's partial dissociation. The formula for pH at the equivalence point can be derived from the concentration of the conjugate base formed. For example, if you have a weak acid HA with a concentration of 0.1 mol/dm³ and a Ka of 1.8 x 10^-5, you can calculate the pH at the equivalence point using the formula: pH = 14 - 0.5 * pKa, where pKa = -log(Ka). Substituting gives pH = 14 - 0.5 * 4.74 = 11.63. Therefore, the pH at the equivalence point is 11.63.
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