Phosphate Buffer Calculator

Henderson-Hasselbalch Equation:

\[ pH = pKa + \log\left(\frac{[A^-]}{[HA]}\right) \]

Calculated pH:

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1. What is the Henderson-Hasselbalch Equation?

The Henderson-Hasselbalch equation is used to estimate the pH of a buffer solution. It relates the pH, pKa (acid dissociation constant), and the ratio of the concentrations of the conjugate base [A⁻] and weak acid [HA] in the solution.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

\[ pH = pKa + \log\left(\frac{[A^-]}{[HA]}\right) \]

Where:

\( pKa \) — Acid dissociation constant
\( [A^-] \) — Concentration of conjugate base (M)
\( [HA] \) — Concentration of weak acid (M)

Explanation: The equation shows that the pH of a buffer solution depends on the pKa of the weak acid and the ratio of base to acid concentrations.

3. Importance of pH Calculation in Buffer Solutions

Details: Accurate pH calculation is crucial for preparing buffer solutions in biochemical and chemical experiments, maintaining stable pH conditions, and understanding acid-base equilibria in biological systems.

4. Using the Calculator

Tips: Enter pKa value, base concentration in M, and acid concentration in M. All concentrations must be positive values greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What is the valid range for the Henderson-Hasselbalch equation?
A: The equation is most accurate when the ratio [A⁻]/[HA] is between 0.1 and 10, and when the concentrations are significantly higher than that of H⁺ and OH⁻ ions.

Q2: Can this equation be used for strong acids or bases?
A: No, the Henderson-Hasselbalch equation is specifically designed for weak acid-base buffer systems.

Q3: What is the significance of pKa in buffer solutions?
A: pKa indicates the pH at which the acid is half-dissociated. Buffers are most effective when pH is within ±1 unit of pKa.

Q4: How does temperature affect the calculation?
A: pKa values are temperature-dependent. For precise calculations, use pKa values measured at the same temperature as your experiment.

Q5: What are common phosphate buffer systems?
A: Phosphate buffers typically use H₂PO₄⁻/HPO₄²⁻ system with pKa around 7.2, making them ideal for biological applications near physiological pH.