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Calcular El Ph Del Acido Acetico 0.1 M

Reviewed by Calculator Editorial Team

Acetic acid (CH3COOH) is a weak organic acid commonly found in vinegar. Calculating its pH at a specific concentration helps understand its acidity level. This guide explains how to determine the pH of 0.1 M acetic acid solution using the Henderson-Hasselbalch equation.

Introduction

The pH of a solution measures its acidity or alkalinity. For weak acids like acetic acid, the pH depends on both the acid concentration and its dissociation constant (Ka). The Henderson-Hasselbalch equation relates these factors to calculate the pH.

Key Point: Acetic acid is a weak acid with a Ka of 1.8 × 10-5 at 25°C. Its pH at 0.1 M concentration is approximately 2.88.

How to Calculate the pH of Acetic Acid

The pH of acetic acid solution can be calculated using the Henderson-Hasselbalch equation:

Henderson-Hasselbalch Equation:

pH = pKa + log10([A-]/[HA])

Where:

  • pKa = -log10(Ka)
  • [A-] = concentration of acetate ion (conjugate base)
  • [HA] = concentration of acetic acid

For a 0.1 M acetic acid solution:

  1. Determine the pKa of acetic acid (typically 4.76 at 25°C)
  2. Assume the solution is at equilibrium, so [A-] = [HA] = 0.1 M
  3. Plug values into the equation: pH = 4.76 + log10(0.1/0.1) = 4.76 + log10(1) = 4.76 + 0 = 4.76

However, since acetic acid is a weak acid, the actual pH is slightly lower due to incomplete dissociation. For more precise calculations, consider the exact dissociation constant.

Example Calculation

Let's calculate the pH of 0.1 M acetic acid solution using the exact Ka value:

  1. Given: Ka = 1.8 × 10-5
  2. Calculate pKa: pKa = -log10(1.8 × 10-5) ≈ 4.746
  3. Assume [A-] = [HA] = 0.1 M at equilibrium
  4. Calculate pH: pH = 4.746 + log10(0.1/0.1) = 4.746 + 0 = 4.746

The calculated pH of 0.1 M acetic acid solution is approximately 4.75.

Note: The actual pH may vary slightly due to temperature effects and solution conditions.

Interpreting the Results

A pH of 4.75 indicates that the solution is acidic, as expected for acetic acid. This value is typical for dilute acetic acid solutions. The result shows that:

  • The solution contains more undissociated acetic acid than acetate ions
  • The acidity is moderate, not strongly acidic or basic
  • The pH is consistent with the weak acid nature of acetic acid

Comparing with other common acids:

Acid pH at 0.1 M Acidity Strength
Acetic Acid 4.75 Weak
Hydrochloric Acid ≈ -1 (strong acid) Strong
Ammonia Solution ≈ 11 (basic) Weak base

Frequently Asked Questions

What is the pH of 0.1 M acetic acid?

The pH of 0.1 M acetic acid solution is approximately 4.75 at 25°C.

Why is acetic acid considered a weak acid?

Acetic acid has a relatively low dissociation constant (Ka ≈ 1.8 × 10-5), meaning it doesn't fully dissociate in water, resulting in a moderate pH.

How does temperature affect the pH of acetic acid?

Temperature increases the Ka of acetic acid, making it more dissociated and slightly lowering the pH.

Can I use the Henderson-Hasselbalch equation for all weak acids?

The equation works best for weak acids with pKa values between 2 and 12. For very weak or very strong acids, other methods may be needed.