Question detail
What is the expected pH at the equivalence point when titrating a strong acid 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. 7
- B. 3
- C. 10
- D. 1
Answer
7
Explanation
At the equivalence point of a strong acid-strong base titration, the resulting solution is neutral, leading to a pH of 7, as the acid and base completely neutralize each other.
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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