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Calculate Ph of 0.010 M Sodium Acetate

Reviewed by Calculator Editorial Team

Sodium acetate (CH₃COONa) is a weak electrolyte that dissociates in water to form acetate ions (CH₃COO⁻) and sodium ions (Na⁺). The pH of a sodium acetate solution depends on its concentration and the dissociation constant of acetic acid (Ka). This calculator helps determine the pH of a 0.010 M sodium acetate solution.

Introduction

Sodium acetate is commonly used as a buffer solution in chemical and biological applications. Understanding its pH is essential for proper experimentation and quality control. The pH of a sodium acetate solution can be calculated using the Henderson-Hasselbalch equation, which relates the pH to the concentration of the conjugate acid and base.

Key Point: Sodium acetate solutions are typically buffered around pH 4.76 due to the dissociation of acetic acid (CH₃COOH) and acetate ions (CH₃COO⁻).

Calculation Method

The pH of a sodium acetate solution can be calculated using the Henderson-Hasselbalch equation:

Henderson-Hasselbalch Equation:

pH = pKa + log10([CH₃COO⁻]/[CH₃COOH])

Where:

  • pKa is the negative logarithm of the acid dissociation constant (Ka) of acetic acid (1.75 × 10⁻⁵ at 25°C)
  • [CH₃COO⁻] is the concentration of acetate ions
  • [CH₃COOH] is the concentration of acetic acid

For a 0.010 M sodium acetate solution, we assume complete dissociation of sodium acetate into acetate ions and sodium ions. The concentration of acetic acid is negligible compared to the acetate ions, so the equation simplifies to:

Simplified Equation:

pH = pKa + log10([CH₃COO⁻]/[CH₃COOH]) ≈ pKa + log10([CH₃COO⁻]/0) ≈ pKa + log10(∞) ≈ pKa + ∞ ≈ ∞

However, in reality, the pH of a 0.010 M sodium acetate solution is approximately 8.76 due to the presence of a small amount of acetic acid formed by the dissociation of water.

Example Calculation

Let's calculate the pH of a 0.010 M sodium acetate solution:

  1. Determine the pKa of acetic acid: pKa = -log(1.75 × 10⁻⁵) ≈ 4.76
  2. Assume complete dissociation of sodium acetate: [CH₃COO⁻] = 0.010 M, [CH₃COOH] ≈ 0 M
  3. Apply the Henderson-Hasselbalch equation: pH = 4.76 + log(0.010/0) ≈ 4.76 + ∞ ≈ ∞
  4. Account for the dissociation of water: pH ≈ 8.76
pH Calculation Summary
Parameter Value
Concentration of CH₃COO⁻ 0.010 M
Concentration of CH₃COOH Negligible
pKa of acetic acid 4.76
Calculated pH ≈8.76

Interpretation

The pH of a 0.010 M sodium acetate solution is approximately 8.76. This indicates a strongly basic solution due to the presence of acetate ions. The solution is buffered around this pH, meaning it resists changes in pH when small amounts of acid or base are added.

Practical Tip: Sodium acetate solutions are often used as buffers in biochemical assays and chemical titrations due to their stable pH around 8.76.

FAQ

What is the pH of a 0.010 M sodium acetate solution?
The pH of a 0.010 M sodium acetate solution is approximately 8.76.
How is the pH of sodium acetate calculated?
The pH is calculated using the Henderson-Hasselbalch equation, which relates the pH to the concentration of acetate ions and acetic acid.
Why is the pH of sodium acetate higher than expected?
The pH is higher than expected due to the dissociation of water, which contributes to the concentration of hydroxide ions in the solution.
Can sodium acetate solutions be used as buffers?
Yes, sodium acetate solutions are often used as buffers in biochemical and chemical applications due to their stable pH around 8.76.