Phosphate Buffer Calculator Ph 7

Henderson-Hasselbalch Equation:

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

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 conjugate acid-base pair H₂PO₄⁻ (dihydrogen phosphate) and HPO₄²⁻ (monohydrogen phosphate), with a pKa₂ value of approximately 7.2 at 25°C.

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:

\( pH \) — The calculated pH value (dimensionless)
\( pKa_2 \) — The acid dissociation constant for H₂PO₄⁻ ⇌ H⁺ + HPO₄²⁻
\( [HPO_4^{2-}] \) — Concentration of monohydrogen phosphate (mol/L)
\( [H_2PO_4^-] \) — Concentration of dihydrogen phosphate (mol/L)

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

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 the pKa₂ value (typically 7.2 for phosphate buffer at 25°C), 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 pKa₂ value for phosphate buffer?
A: The pKa₂ for the phosphate buffer system is approximately 7.2 at 25°C, but it can vary slightly with temperature and ionic strength.

Q2: What is the optimal buffer 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 7.2.

Q3: Why is phosphate buffer important in biological systems?
A: Phosphate buffer is crucial for maintaining intracellular pH and is involved in many biochemical processes, including energy metabolism and signal transduction.

Q4: How does temperature affect the pKa value?
A: The pKa of phosphate buffer decreases slightly with increasing temperature, typically by about 0.0028 units per °C.

Q5: Can this calculator be used for other buffer systems?
A: While the Henderson-Hasselbalch equation is general, this calculator is specifically designed for the phosphate buffer system with its characteristic pKa₂ value.