Question detail
Sketch the pH curve for the titration of a weak monoprotic acid with a strong base. Explain the key features of the curve.
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
Question
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exam_style
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Topic
Acids and bases (A-level only)
Question
Sketch the pH curve for the titration of a weak monoprotic acid with a strong base. Explain the key features of the curve.
Answer
The pH curve will show a gradual increase in pH at first, followed by a steep rise near the equivalence point, and then a plateau as the strong base is added. The equivalence point will occur at a pH greater than 7 due to the weak acid's incomplete dissociation.
Explanation
This answer is strong because it accurately describes the shape of the pH curve and identifies the significance of the equivalence point. The question tests the student's understanding of the behavior of weak acids during titration with strong bases.
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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