1. What is the Henderson-Hasselbalch Equation?

The Henderson-Hasselbalch equation relates the pH of a solution to the pKa of the acid and the ratio of the concentrations of the conjugate base and acid. It's particularly useful for buffer solutions like monosodium phosphate buffers.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

Where:

• \( pH \) — The calculated pH of the buffer solution
• \( pKa \) — Acid dissociation constant of the weak acid
• \( [base] \) — Concentration of the conjugate base (Na2HPO4)
• \( [acid] \) — Concentration of the weak acid (NaH2PO4)

Explanation: The equation shows that buffer pH depends on the ratio of base to acid concentrations, not their absolute values.

3. Importance of pH Calculation

Details: Accurate pH calculation is crucial for preparing buffer solutions in biochemical and pharmaceutical applications where maintaining stable pH is essential.

4. Using the Calculator

Tips: Enter the pKa value (7.21 for phosphate buffer at 25°C), concentrations of base and acid in mol/L. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the pKa value for monosodium phosphate buffer?
A: The pKa for the H2PO4-/HPO4²- system is 7.21 at 25°C, but this varies slightly with temperature and ionic strength.

Q2: What is the effective buffer range?
A: The phosphate buffer is most effective in the pH range of 6.2-8.2 (pKa ± 1).

Q3: How does temperature affect the calculation?
A: Temperature affects both pKa and pH measurements. For precise work, use temperature-corrected pKa values.

Q4: What are common uses of phosphate buffers?
A: They're widely used in biological research, medical diagnostics, and pharmaceutical preparations.

Q5: Can I use this for other buffer systems?
A: Yes, the equation is general, but you need the correct pKa for your specific acid-base pair.