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

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

3. Importance of Buffer pH Calculation

Details: Accurate pH calculation is crucial for preparing buffer solutions in biochemical experiments, pharmaceutical formulations, and various industrial processes where maintaining a stable pH is essential.

4. Using the Calculator

Tips: Enter pKa value, concentrations of conjugate base [A⁻] and weak acid [HA] in mol/L. All concentration values must be positive numbers greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What is the valid range for the Henderson-Hasselbalch equation?
A: The equation works best when the ratio [A⁻]/[HA] is between 0.1 and 10, which corresponds to pH values within approximately pKa ± 1 unit.

Q2: When is the Henderson-Hasselbalch equation not accurate?
A: The equation may be less accurate for very dilute solutions, strong acids/bases, or when the concentrations of [A⁻] and [HA] differ by several orders of magnitude.

Q3: What are common buffer systems that follow this equation?
A: Common buffer systems include acetate (acetic acid/acetate), phosphate (H₂PO₄⁻/HPO₄²⁻), and Tris (TrisHCl/Tris base) buffers.

Q4: How does temperature affect the calculation?
A: Temperature affects the pKa value of the acid. The pKa input should be the value at the temperature of interest for accurate results.

Q5: Can this equation be used for polyprotic acids?
A: For polyprotic acids, the equation can be applied to each dissociation step separately, considering the appropriate pKa and concentration ratios for each step.