1. What is the Henderson-Hasselbalch Equation?

The Henderson-Hasselbalch equation is used to estimate the pH of a buffer solution. It relates the pH, pKa (acid dissociation constant), and the ratio of the concentrations of the conjugate base [A⁻] and weak acid [HA].

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

For this specific case with equal concentrations (0.1 M) of acid and conjugate base:

• \( [A^-] = 0.1 \) mol/L (conjugate base concentration)
• \( [HA] = 0.1 \) mol/L (weak acid concentration)
• \( pKa \) — Acid dissociation constant (dimensionless)

Explanation: When the concentrations of acid and conjugate base are equal, the log term becomes zero, resulting in pH = pKa.

3. Importance of pH Calculation

Details: Accurate pH calculation is crucial for understanding buffer capacity, predicting chemical behavior, and maintaining stable pH conditions in biological and chemical systems.

4. Using the Calculator

Tips: Enter the pKa value (dimensionless). The concentration is fixed at 0.1 M for both acid and conjugate base components.

5. Frequently Asked Questions (FAQ)

Q1: Why does pH equal pKa when concentrations are equal?
A: When [A⁻] = [HA], the log([A⁻]/[HA]) term becomes log(1) = 0, simplifying the equation to pH = pKa.

Q2: What is the significance of 0.1 M concentration?
A: 0.1 M is a common concentration used in buffer preparations, providing good buffering capacity while maintaining reasonable solute concentrations.

Q3: When is this calculation most accurate?
A: This calculation is most accurate when the acid is weak and the concentrations are not too dilute (typically > 0.01 M).

Q4: Are there limitations to this equation?
A: The equation assumes ideal behavior and may be less accurate for very concentrated solutions or when ionic strength effects are significant.

Q5: Can this be used for polyprotic acids?
A: For polyprotic acids, the calculation becomes more complex and typically focuses on one dissociation step at a time.