Textbook Question
On the same graph, sketch pH titration curves for the titra-tion of (1) a strong acid with a strong base and (2) a weak acid with a strong base. How do the two curves differ with respect to the following? (a) The initial pH
18. Aqueous Equilibrium
Intro to Acid-Base Titration Curves
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When comparing titration curves for two acids with different pKa values, which of the following statements is true?
A
The acid with the lower pKa will have a higher pH at the start of the titration.
B
The acid with the lower pKa will have a steeper initial slope.
C
The acid with the higher pKa will reach the equivalence point first.
D
Both acids will have the same pH at the equivalence point.
Verified step by step guidance1
Understand that pKa is a measure of the strength of an acid; a lower pKa value indicates a stronger acid.
Recognize that during a titration, the initial slope of the titration curve is influenced by the strength of the acid. A stronger acid (lower pKa) will dissociate more completely, leading to a steeper initial slope.
Consider the equivalence point, which is reached when the amount of titrant added is stoichiometrically equivalent to the amount of acid present. The position of the equivalence point on the pH scale is not directly determined by the pKa.
Note that the pH at the equivalence point is determined by the nature of the salt formed and the strength of the conjugate base, not by the initial pKa of the acid.
Conclude that the statement 'The acid with the lower pKa will have a steeper initial slope' is true, as a stronger acid will show a more pronounced change in pH with the addition of titrant at the start of the titration.
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