Phosphate Buffer Calculator Ph 8

Henderson-Hasselbalch Equation:

\[ pH = pKa_2 + \log\left(\frac{[HPO_4^{2-}]}{[H_2PO_4^-]}\right) \]

pKa 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 maintains pH stability in cells and bodily fluids. It consists of the conjugate acid-base pair H₂PO₄⁻ (dihydrogen phosphate) and HPO₄²⁻ (monohydrogen phosphate).

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

\[ pH = pKa_2 + \log\left(\frac{[HPO_4^{2-}]}{[H_2PO_4^-]}\right) \]

Where:

\( pH \) — Calculated pH value (dimensionless)
\( pKa_2 \) — Acid dissociation constant for H₂PO₄⁻/HPO₄²⁻ system (≈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 optimal conditions for enzymatic reactions, and understanding acid-base balance in physiological systems.

4. Using the Calculator

Tips: Enter pKa 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: What is the typical pKa value for phosphate buffer?
A: The second pKa (pKa₂) for phosphoric acid is approximately 7.2 at 25°C, which makes phosphate buffer effective in the physiological pH range.

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

Q3: Why is phosphate buffer important in biological systems?
A: Phosphate is a major intracellular buffer and plays a crucial role in maintaining pH stability in cells, blood, and other biological fluids.

Q4: Are there limitations to phosphate buffer?
A: Phosphate buffer can precipitate with calcium ions, may inhibit some enzymatic reactions, and has limited capacity outside its optimal pH range.

Q5: How does temperature affect pKa values?
A: pKa values are temperature-dependent. The pKa₂ of phosphate decreases by about 0.0028 units per degree Celsius increase in temperature.