Question

A buffer contains significant amounts of acetic acid and sodium acetate. Write equations showing how this buffer neutralizes added acid and added base.

Short answer

Acid is neutralized by the reaction: \( CH3COO^- + H^+ \rightarrow CH3COOH \). Base is neutralized by the reaction: \( CH3COOH + OH^- \rightarrow CH3COO^- + H2O \).

Step-by-step solution

Neutralization of Added Acid

When an acid is added to the buffer solution, the acetic acid (CH3COOH) does not react, because it's the weak acid component of the buffer. However, the added acid (H+) will react with the conjugate base, namely the acetate ion (CH3COO-) from sodium acetate. Acetate ions will combine with the hydrogen ions to form more acetic acid. The equation representing this reaction is: \( CH3COO^- + H^+ \rightarrow CH3COOH \).

Neutralization of Added Base

When a base is added to the buffer solution, the sodium acetate (CH3COONa) largely remains unchanged, but the acetic acid will react with the added base. Specifically, the hydroxide ions (OH-) from the added base will react with acetic acid to form water and acetate ions. The equation for this reaction is: \( CH3COOH + OH^- \rightarrow CH3COO^- + H2O \).

Key concepts

Acid-Base Neutralization

Understanding how a buffer solution works involves recognizing the key role of acid-base neutralization. This process is essential in maintaining the pH level of a system. When either an acid or base is introduced into a buffer solution, a reaction occurs that minimizes the change in pH.

For instance, with a buffer containing acetic acid and sodium acetate, if you add an acid to the mix, the hydrogen ions (\(H^+\) ions) are quickly sequestered by the acetate ions (\(CH3COO^-\) ions), forming more acetic acid. This keeps the pH from dropping significantly. Conversely, if a base is introduced, the hydroxide ions (\(OH^-\) ions) react with acetic acid to produce water and acetate ions, preventing a substantial rise in pH. These reactions demonstrate how the buffer neutralizes added substances, keeping the system stable.

Conjugate Acid-Base Pairs

The concept of conjugate acid-base pairs is crucial in buffer chemistry. A conjugate acid-base pair consists of two species that transform into each other by the gain or loss of a proton (\(H^+\)).

In the buffer system from our exercise, acetic acid (\(CH3COOH\)) and its conjugate base, acetate ion (\(CH3COO^-\)), work together to neutralize added acids or bases. When acetic acid loses a proton, it becomes acetate ion, and when acetate gains a proton, it becomes acetic acid. This reversible action allows the buffer to absorb excess hydrogen or hydroxide ions without significantly altering the overall pH of the solution.

Buffer Capacity

The buffer capacity refers to the amount of acid or base that can be added to a buffer solution before a significant change in pH occurs. It's dependent on the amounts of the weak acid and its conjugate base present in the solution. A buffer with a high concentration of these two components will have a greater buffer capacity, meaning it can neutralize more added acid or base without a large shift in pH.

Buffer capacity is inherently linked to the concept of acid-base neutralization. The larger the reservoir of the acid and conjugate base, the more 'neutralization power' the buffer possesses. Hence, to maximize the buffer capacity, you would want a high concentration of both components—a fine balance between acetic acid and sodium acetate is essential in our example buffer solution.