The formation of a buffer solution is a critical concept in understanding the behavior of weak acids and their conjugate bases. This guide explains how a 1 M solution of acetic acid (CH3COOH) can form a buffer with 0.5 M sodium hydroxide (NaOH).

Understanding Buffer Solutions

A buffer solution is a solution that resists changes in pH when small amounts of strong acid or base are added. A buffer typically consists of a weak acid and its conjugate base. The conjugate base is formed when the weak acid reacts with a base.

Components of the Buffer System

In this scenario, we have:

Stoichiometry and Reaction Dynamics

The reaction between acetic acid and sodium hydroxide follows the equation:

CH3COOH NaOH → CH3COONa H2O

When 0.5 M of NaOH is added to 1 M CH3COOH, the reaction will proceed until the moles of NaOH match the moles of CH3COOH.

Post-Reaction Analysis

Let's break down the reaction:

The reaction will consume 0.5 M of CH3COOH, leaving 0.5 M of CH3COOH unreacted. The 0.5 M of NaOH will completely react, forming 0.5 M of CH3COONa.

Now we have:

Proper Buffer Formation

When a weak acid and its conjugate base are present in comparable concentrations, such as 0.5 M each, they form an effective buffer solution.

This buffer system will have a pH close to the pKa of acetic acid, which is approximately 4.74. In this case, the resulting buffer will have a pH of 4.74, which is the pKa of CH3COOH.

This buffer has maximum buffering capacity under these conditions. You can adjust the pH of the buffer by changing the ratio of CH3COOH to CH3COONa. The exact ratio can be calculated using the Henderson-Hasselbalch equation.

Example Calculation: Using the Henderson-Hasselbalch equation:

pH pKa log([A-]/[HA])

For a pH of 4.74 (the pKa of acetic acid) and a buffer with maximum capacity:

4.74 4.74 log([CH3COONa]/[CH3COOH])

This implies an equal concentration of CH3COOH and CH3COONa, which is our case (0.5 M each).

Conclusion

Yes, a 1 M CH3COOH solution can form a buffer with a 0.5 M NaOH solution. This results in a buffer with a pH of 4.74, ideal for various chemical applications and industrial processes.

Verification and Application

To ensure the buffer is effective, you can verify its capacity by adding small amounts of strong acids or bases and observing the pH change. This buffer is particularly useful in biological and chemical experiments where maintaining a stable pH is crucial.

By understanding and applying the principles of buffer formation, you can effectively manage pH in diverse experimental and industrial settings.