Phosphate Buffer Solution Calculator

Henderson-Hasselbalch Equation for Phosphate Buffer:

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

Calculated pH:

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1. What is the Phosphate Buffer System?

The phosphate buffer system is an important buffer in biological systems, particularly in intracellular fluid and renal tubules. It consists of dihydrogen phosphate (H₂PO₄^-) as the weak acid and hydrogen phosphate (HPO₄^2-) as the conjugate base.

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:

\( pH \) — Resulting pH of the buffer solution
\( pKa_2 \) — Acid dissociation constant for the second dissociation of phosphoric acid (typically 7.21 at 25°C)
\( [HPO_4^{2-}] \) — Concentration of dibasic phosphate (mol/L)
\( [H_2PO_4^-] \) — Concentration of monobasic 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 weak acid.

3. Importance of Phosphate Buffer

Details: The phosphate buffer system is crucial in biological systems, particularly in maintaining intracellular pH and in renal excretion of hydrogen ions. It's also commonly used in laboratory settings for biochemical experiments.

4. Using the Calculator

Tips: Enter the pKa₂ value (typically 7.21 at 25°C), the concentrations of both phosphate species in mol/L. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical pKa₂ value for phosphate buffer?
A: The second pKa for phosphoric acid is approximately 7.21 at 25°C, but this can vary slightly with temperature and ionic strength.

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

Q3: Why is phosphate buffer important in biological systems?
A: It's abundant in cells and can buffer pH changes effectively in the physiological range. It's particularly important in renal tubular fluid and intracellular fluid.

Q4: How does temperature affect the pKa of phosphate buffer?
A: The pKa decreases slightly with increasing temperature (about -0.0028 units per °C for pKa₂).

Q5: Can I use this calculator for other buffer systems?
A: This specific calculator is designed for the phosphate buffer system. Other buffer systems would require their specific pKa values.