The following pictures represent initial concentrations in solutions that contain a weak acid HA (pKa = 6.0) and its sodium salt NaA. (Na+ ions and solvent water molecules have been omitted for clarity.)

. (b) Draw a picture that represents the equilibrium state of solution (1) after the addition of two H3O+ ions.

Verified step by step guidance

1. Identify the components in the solution: HA (weak acid) and A⁻ (conjugate base).
2. Recognize that adding H₃O⁺ ions will shift the equilibrium towards the formation of more HA, as per Le Chatelier's principle.
3. In the initial state (image 1), count the number of HA and A⁻ particles to understand the starting concentrations.
4. After adding two H₃O⁺ ions, expect two A⁻ ions to react with H₃O⁺ to form two additional HA molecules.
5. Draw the new equilibrium state by increasing the number of HA molecules by two and decreasing the number of A⁻ ions by two.

Key Concepts

Weak Acids and Their Equilibrium

Weak acids, like HA, do not fully dissociate in solution, establishing an equilibrium between the undissociated acid and its ions. The equilibrium constant, Ka, quantifies this balance, and the pKa value indicates the strength of the acid. A lower pKa means a stronger acid, while a higher pKa indicates a weaker acid.

H3O+ Ion Addition

Adding H3O+ ions to a solution containing a weak acid shifts the equilibrium according to Le Chatelier's principle. This principle states that if a system at equilibrium is disturbed, it will adjust to counteract the disturbance. In this case, the addition of H3O+ will favor the formation of more undissociated acid (HA) from its ions (A-).

Equilibrium Representation in Diagrams

Diagrams representing chemical equilibria visually depict the relative concentrations of reactants and products. In the context of weak acids, these diagrams can illustrate the distribution of HA and A- before and after the addition of H3O+ ions, helping to conceptualize how the equilibrium shifts and the resulting changes in concentration.