1. What is the Henderson-Hasselbalch Equation?

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

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

Where:

• \( pH \) — pH value of the buffer solution
• \( pKa \) — Acid dissociation constant
• \( [base] \) — Concentration of conjugate base (mol/L)
• \( [acid] \) — Concentration of weak acid (mol/L)

Explanation: The equation demonstrates that the pH of a buffer solution depends on the pKa of the weak acid and the ratio of base to acid concentrations.

3. Importance of pH Calculation

Details: Accurate pH calculation is crucial for preparing buffer solutions in biochemical experiments, pharmaceutical formulations, and various laboratory applications where maintaining specific pH levels is essential.

4. Using the Calculator

Tips: Enter pKa value, base concentration in mol/L, and acid concentration in mol/L. All values must be valid (concentrations > 0).

5. Frequently Asked Questions (FAQ)

Q1: What is the typical pKa value for phosphate buffer?
A: The phosphate buffer system has three pKa values: pKa₁ = 2.14, pKa₂ = 7.20, pKa₃ = 12.67. The most commonly used is pKa₂ = 7.20 for physiological pH ranges.

Q2: What are the limitations of the Henderson-Hasselbalch equation?
A: The equation assumes ideal behavior and may not be accurate at very high or very low concentrations, or when ionic strength significantly affects the activity coefficients.

Q3: What is the effective buffer range?
A: A buffer is most effective when pH = pKa ± 1. Outside this range, the buffer capacity decreases significantly.

Q4: Can this equation be used for polyprotic acids?
A: For polyprotic acids like phosphoric acid, the equation can be applied to each dissociation step separately when the pKa values are sufficiently separated.

Q5: How does temperature affect pKa values?
A: pKa values are temperature-dependent. For accurate calculations, use pKa values measured at the same temperature as your experimental conditions.