19 Calculate The Ph of A 0.36 M Ch3coona Solution

Introduction

The pH of a solution is a measure of its acidity or basicity. For a solution of sodium acetate (CH₃COONa), the pH can be calculated using the Henderson-Hasselbalch equation, which relates the pH to the concentration of the conjugate acid and base.

Sodium acetate is a weak base, meaning it partially dissociates in water. The dissociation reaction is:

When sodium acetate dissolves in water, it forms acetate ions and hydroxide ions. The concentration of hydroxide ions determines the pH of the solution.

Formula

The pH of a sodium acetate solution can be calculated using the following formula:

Where:

• pK_b is the base dissociation constant for acetate (approximately 4.75)
• [CH₃COO^-] is the concentration of acetate ions
• [CH₃COOH] is the concentration of acetic acid

For a 0.36 M sodium acetate solution, the concentration of acetate ions is equal to the concentration of sodium acetate because it fully dissociates in water. The concentration of acetic acid is negligible in this case.

Calculation

To calculate the pH of a 0.36 M sodium acetate solution:

1. Identify the pK_b value for acetate, which is approximately 4.75.
2. Determine the concentration of acetate ions, which is equal to the concentration of sodium acetate (0.36 M).
3. Assume the concentration of acetic acid is negligible (0 M).
4. Plug these values into the Henderson-Hasselbalch equation:

Since the concentration of acetic acid is negligible, the term log₁₀(0.36/0) approaches infinity. This means the pH of a 0.36 M sodium acetate solution is very high, indicating a strongly basic solution.

Interpretation

The pH of a 0.36 M sodium acetate solution is approximately 14, which indicates a strongly basic solution. This is because sodium acetate fully dissociates in water, forming a high concentration of hydroxide ions.

In practical terms, a pH of 14 means the solution is highly alkaline and can react strongly with acidic substances. It is important to handle sodium acetate solutions with care to avoid skin and eye irritation.