1. What is the Sodium Phosphate Buffer pH 7 Calculator?

The Sodium Phosphate Buffer pH 7 Calculator estimates the pH of a phosphate buffer solution using the Henderson-Hasselbalch equation. It calculates pH based on the pKa2 value and the concentrations of HPO₄²⁻ and H₂PO₄⁻ ions.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

Where:

• \( pH \) — pH value (dimensionless)
• \( pKa2 \) — Acid dissociation constant for H₂PO₄⁻ ⇌ H⁺ + HPO₄²⁻ (dimensionless)
• \( [HPO_4^{2-}] \) — Concentration of hydrogen phosphate ion (mol/L)
• \( [H_2PO_4^{-}] \) — Concentration of dihydrogen phosphate ion (mol/L)

Explanation: The equation relates the pH of a buffer solution to the pKa of the acid and the ratio of the concentrations of the conjugate base and acid.

3. Importance of pH Calculation

Details: Accurate pH calculation is crucial for preparing buffer solutions in biochemical and pharmaceutical applications, maintaining optimal conditions for enzymatic reactions, and ensuring stability of biological samples.

4. Using the Calculator

Tips: Enter pKa2 value (typically 7.2 for phosphate buffer), concentrations of HPO₄²⁻ and H₂PO₄⁻ in mol/L. All concentration values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical pKa2 value for phosphate buffer?
A: The pKa2 for the H₂PO₄⁻/HPO₄²⁻ system is typically 7.2 at 25°C, though it can vary slightly with temperature and ionic strength.

Q2: Why is pH 7 important for phosphate buffers?
A: pH 7 is physiologically relevant and phosphate buffers are particularly effective near their pKa2 value (7.2), providing good buffering capacity around pH 7.

Q3: What are the units for concentration inputs?
A: Concentrations should be entered in mol/L (molarity). Ensure both concentrations are in the same units.

Q4: Are there limitations to this calculation?
A: The calculation assumes ideal behavior and may be less accurate at very high concentrations or extreme pH values where activity coefficients differ significantly.

Q5: How does temperature affect the calculation?
A: pKa2 values are temperature-dependent. For precise work, use pKa2 values appropriate for your experimental temperature.