The following pictures represent solutions that contain one or more of the compounds H2A, NaHA, and Na2A, where H2A is a weak diprotic acid. (Na+ ions and solvent water molecules have been omitted for clarity.)

(b) Which solution has the greatest buffer capacity?

Verified step by step guidance

1. Identify the components of each solution: H2A, NaHA, and Na2A.
2. Understand that a buffer solution consists of a weak acid and its conjugate base.
3. Recognize that the greatest buffer capacity is achieved when the concentrations of the weak acid and its conjugate base are equal.
4. Analyze the images to determine the relative concentrations of H2A, NaHA, and Na2A in each solution.
5. Select the solution where the concentrations of the weak acid (H2A) and its conjugate base (NaHA) are closest to being equal.

Key Concepts

Buffer Capacity

Buffer capacity refers to the ability of a solution to resist changes in pH upon the addition of small amounts of acid or base. It is determined by the concentration of the weak acid and its conjugate base present in the solution. A higher concentration of these components typically results in greater buffer capacity, allowing the solution to maintain a stable pH.

Weak Diprotic Acid

A weak diprotic acid, such as H2A, can donate two protons (H+) in a stepwise manner. The first dissociation produces a conjugate base (HA-), while the second dissociation produces a further conjugate base (A2-). The presence of both the weak acid and its conjugate bases in solution is crucial for effective buffering, as they can neutralize added acids or bases.

Equilibrium and Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is disturbed, the system will adjust to counteract the disturbance and restore a new equilibrium. In the context of buffer solutions, adding an acid or base shifts the equilibrium between the weak acid and its conjugate base, allowing the buffer to maintain pH stability. Understanding this principle is essential for predicting how different buffer solutions will respond to pH changes.