What does pKa indicate about an acid?

The pKa value is a critical concept in understanding acid strength in aqueous chemistry. It represents the strength of an acid as derived from its dissociation constant (Ka). The dissociation constant measures how completely an acid releases its protons (H+) in solution. A lower pKa value indicates a stronger acid, as this corresponds to a higher Ka, meaning more of the acid dissociates into its ions in solution.

In more practical terms, when comparing different acids, the one with the lower pKa value is the stronger acid, as it indicates a greater tendency to lose protons. This makes pKa a more convenient scale for comparing acid strengths than using Ka directly, especially since pKa is on a logarithmic scale. For these reasons, the correct answer highlights the relationship between pKa, acid strength, and the acid's dissociation constant, making it a fundamental aspect of acid-base chemistry.