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 (the acid dissociation constant), and the ratio of the concentrations of the conjugate base and weak acid in the solution.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

Where:

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

3. Importance of pH Calculation in Buffer Solutions

Details: Accurate pH calculation is crucial for understanding buffer capacity, preparing buffer solutions with specific pH values, and predicting how a buffer will respond to added acid or base.

4. Using the Calculator

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

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 [base]/[acid] is between 0.1 and 10, and when the concentrations are significantly higher than that of H+ and OH- ions.

Q2: Can this equation be used for all buffer systems?
A: The equation works best for weak acid/conjugate base pairs where the acid dissociation follows ideal behavior. It may be less accurate for very concentrated solutions or polyprotic acids.

Q3: What are typical pKa values for common buffers?
A: Common buffers have pKa values near the desired pH. For example, acetate buffer (pKa = 4.76), phosphate buffer (pKa = 7.2), and Tris buffer (pKa = 8.06).

Q4: How does temperature affect the calculation?
A: pKa values are temperature-dependent. For precise work, use pKa values measured at the temperature of interest.

Q5: What are the limitations of the Henderson-Hasselbalch equation?
A: The equation assumes ideal behavior, neglects activity coefficients, and may be inaccurate for very dilute or concentrated solutions, or when the [base]/[acid] ratio is extreme.