The following diagrams represent aqueous solutions of three acids, HX, HY, and HZ. The water molecules have been omitted for clarity, and the hydrated proton is represented as H+ rather than H3O+.(b) Which acid would have the smallest aciddissociation constant, Ka?

Key Concepts

Acid Dissociation Constant (Ka)

The acid dissociation constant, Ka, quantifies the strength of an acid in solution. It is defined as the equilibrium constant for the dissociation of an acid into its conjugate base and a proton (H+). A higher Ka value indicates a stronger acid that dissociates more completely in solution, while a lower Ka value suggests a weaker acid with less dissociation.

Strength of Acids

The strength of an acid is determined by its ability to donate protons (H+) in an aqueous solution. Strong acids, such as hydrochloric acid (HCl), dissociate completely, while weak acids, like acetic acid (CH3COOH), only partially dissociate. The relative strength of the acids represented in the diagrams can be inferred from their molecular structures and the presence of electronegative atoms that stabilize the conjugate base.

Molecular Structure and Electronegativity

The molecular structure of an acid, including the presence of electronegative atoms, significantly influences its acidity. Electronegativity affects the stability of the conjugate base formed after dissociation; more electronegative atoms can stabilize negative charge better, leading to a stronger acid. Analyzing the diagrams, one can assess which acid has a structure that would likely result in a lower Ka value based on these principles.