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 solution.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

Where:

• \( pH \) — The calculated pH 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 weak acid.

3. Importance of Buffer pH Calculation

Details: Buffer solutions resist changes in pH when small amounts of acid or base are added. Accurate pH calculation is crucial in chemical, biological, and pharmaceutical applications where maintaining a stable pH is essential.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

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

Q2: Can this equation be used for all buffer systems?
A: The equation works best for weak acid buffers where the concentrations of [A⁻] and [HA] are much larger than the concentration of H⁺ or OH⁻ ions.

Q3: What are common buffer systems that follow this equation?
A: Common examples include acetate buffer (acetic acid/acetate), phosphate buffer (H₂PO₄⁻/HPO₄²⁻), and bicarbonate buffer (H₂CO₃/HCO₃⁻).

Q4: How does temperature affect the calculation?
A: Temperature affects the pKa value of the acid. The pKa used in calculations should be appropriate for the temperature at which the buffer is used.

Q5: What are the limitations of the Henderson-Hasselbalch equation?
A: The equation assumes ideal behavior and may not be accurate for very concentrated solutions, for buffers with polyprotic acids, or when the pH is far from the pKa.