1. What is the Henderson-Hasselbalch Equation?

The Henderson-Hasselbalch equation is used to estimate the pH of buffer solutions. For sodium phosphate buffers, it relates the pH to the pKa of the phosphate system and the ratio of conjugate base to acid concentrations.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

Where:

• \( pH \) — Resulting pH of the buffer solution (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 buffer pH depends on the pKa value and the logarithm of the base-to-acid concentration ratio.

3. Importance of pH Calculation in Buffer Solutions

Details: Accurate pH calculation is crucial for preparing buffer solutions with desired properties for biochemical experiments, pharmaceutical formulations, and various laboratory applications where stable pH maintenance is required.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: What are the typical pKa values for phosphate buffers?
A: Phosphate buffers have three pKa values: pKa₁ ≈ 2.15, pKa₂ ≈ 7.20, pKa₃ ≈ 12.35. The second pKa is most commonly used for biological buffers.

Q2: What is the effective buffer range for phosphate buffers?
A: Phosphate buffers are most effective in the pH range of approximately 6.2-8.2, centered around pKa₂ ≈ 7.20.

Q3: Why is the base/acid ratio important?
A: The ratio determines the buffer capacity and the exact pH value. A 1:1 ratio gives pH = pKa and maximum buffer capacity.

Q4: Are there limitations to this equation?
A: The equation assumes ideal behavior and may be less accurate at very high or low concentrations, or when ionic strength effects are significant.

Q5: Can this calculator be used for other buffer systems?
A: Yes, the Henderson-Hasselbalch equation applies to any acid-base buffer system, though you must use the appropriate pKa value for that specific acid.