Phosphate Buffer Calculator Ph 7.5

Henderson-Hasselbalch Equation:

\[ pH = pKa2 + \log\left(\frac{[HPO_4^{2-}]}{[H_2PO_4^{-}]}\right) \]

pKa2 Value:

(dimensionless)

[HPO₄²⁻] Concentration:

mol/L

[H₂PO₄⁻] Concentration:

mol/L

Calculated pH:

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1. What is the Phosphate Buffer System?

The phosphate buffer system is an important biological buffer that helps maintain pH stability in cells and bodily fluids. It consists of the weak acid H₂PO₄⁻ (dihydrogen phosphate) and its conjugate base HPO₄²⁻ (monohydrogen phosphate).

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

\[ pH = pKa2 + \log\left(\frac{[HPO_4^{2-}]}{[H_2PO_4^{-}]}\right) \]

Where:

\( pH \) — Calculated pH value (dimensionless)
\( pKa2 \) — Acid dissociation constant for H₂PO₄⁻/HPO₄²⁻ system (typically 7.2)
\( [HPO_4^{2-}] \) — Concentration of monohydrogen phosphate (mol/L)
\( [H_2PO_4^{-}] \) — Concentration of dihydrogen phosphate (mol/L)

Explanation: The equation calculates the pH of a phosphate buffer solution based on the ratio of conjugate base to weak acid concentrations.

3. Importance of pH Calculation

Details: Accurate pH calculation is crucial for preparing biological buffers, maintaining proper cellular function, and ensuring optimal conditions for biochemical reactions and experiments.

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 numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is pKa2 typically 7.2 for phosphate buffer?
A: The pKa2 value of 7.2 represents the dissociation constant for the H₂PO₄⁻/HPO₄²⁻ equilibrium at 25°C, making it ideal for buffering near physiological pH.

Q2: What is the effective buffering range for phosphate buffer?
A: Phosphate buffer is most effective in the pH range of 6.2-8.2, with optimal buffering capacity at pH 7.2.

Q3: When should phosphate buffer be used?
A: Phosphate buffer is commonly used in biological research, clinical diagnostics, and biochemical experiments where pH stability around 7.5 is required.

Q4: Are there limitations to phosphate buffer?
A: Phosphate buffer may precipitate with calcium ions, can promote bacterial growth, and may interfere with some enzymatic reactions.

Q5: How does temperature affect pKa2?
A: The pKa2 value decreases slightly with increasing temperature (approximately -0.0028 units per °C), which should be considered for precise applications.