Consider the titration curves (labeled a and b) for two weak acids, both titrated with 0.100 M NaOH.
(ii) Which acid has the larger Ka?

Verified step by step guidance

1. Identify the titration curves for the two weak acids labeled 'a' and 'b'.
2. Understand that the titration curve of a weak acid with a strong base like NaOH will have a characteristic shape, starting with a low pH and gradually increasing as the base is added.
3. Recognize that the point where the curve is steepest is the equivalence point, where the amount of acid equals the amount of base added.
4. Determine the pH at the half-equivalence point for each curve, which is the point where half of the acid has been neutralized. At this point, the pH equals the pKa of the acid.
5. Compare the pKa values for the two acids. The acid with the lower pKa value has the larger Ka, as pKa and Ka are inversely related (pKa = -log(Ka)).

Key Concepts

Weak Acids and Ka

Weak acids are substances that partially dissociate in solution, establishing an equilibrium between the undissociated acid and its ions. The acid dissociation constant (Ka) quantifies the strength of a weak acid; a larger Ka value indicates a stronger acid that dissociates more in solution. Understanding the relationship between Ka and the titration curve is essential for determining which acid is stronger.

Titration Curves

Titration curves graph the pH of a solution as a function of the volume of titrant added. For weak acids, the curve typically shows a gradual increase in pH, with a steep rise near the equivalence point. The shape and position of the curve can provide insights into the acid's strength and its dissociation behavior, which are critical for comparing the strengths of different weak acids.

Equivalence Point

The equivalence point in a titration is reached when the amount of titrant added is stoichiometrically equivalent to the amount of substance being titrated. For weak acids, this point is characterized by a significant change in pH, which can be influenced by the strength of the acid. Analyzing the pH at the equivalence point helps determine the relative strengths of the acids involved in the titration.