Henderson-Hasselbalch Equation Calculator

Henderson-Hasselbalch Equation:

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

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⁻] to the 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:

\( pH \) — pH value (dimensionless)
\( pKa \) — Acid dissociation constant (dimensionless)
\( [A⁻] \) — Concentration of conjugate base (mol/L)
\( [HA] \) — Concentration of weak acid (mol/L)

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

3. Importance of pH Calculation

Details: Accurate pH calculation is crucial for understanding buffer capacity, predicting chemical behavior in biological systems, and designing experiments in biochemistry and analytical chemistry.

4. Using the Calculator

Tips: Enter pKa value, concentrations of conjugate base [A⁻] and weak acid [HA] in mol/L. All concentration values must be positive numbers greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: When is the Henderson-Hasselbalch equation valid?
A: The equation is most accurate when the concentrations of [A⁻] and [HA] are within an order of magnitude of each other (0.1 < [A⁻]/[HA] < 10).

Q2: What are typical pKa values for common buffers?
A: Acetic acid: 4.76, Phosphoric acid (pKa2): 7.20, Tris: 8.08, Bicarbonate: 6.35 (pKa1) and 10.33 (pKa2).

Q3: Can this equation be used for strong acids or bases?
A: No, the Henderson-Hasselbalch equation is specifically designed for weak acid-base systems and buffer solutions.

Q4: What are the limitations of this equation?
A: The equation assumes ideal behavior and may not be accurate at very high or very low concentrations, or when ionic strength effects are significant.

Q5: How is this equation used in biological systems?
A: It's widely used to calculate and maintain pH in biological buffers, cell culture media, and pharmaceutical formulations.