1. What is the Henderson-Hasselbalch Equation?

The Henderson-Hasselbalch equation relates pH, pKa (acid dissociation constant), and the ratio of concentrations of a weak acid and its conjugate base in solution. It's widely used in chemistry and biochemistry to calculate pH or pKa in buffer systems.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

Where:

• \( pKa \) — Acid dissociation constant (dimensionless)
• \( pH \) — Negative log of hydrogen ion concentration (dimensionless)
• \( [base] \) — Concentration of conjugate base (mol/L)
• \( [acid] \) — Concentration of weak acid (mol/L)

Explanation: The equation shows that pKa can be calculated from pH when the ratio of base to acid concentrations is known.

3. Importance of pKa Calculation

Details: pKa values are crucial for understanding acid-base chemistry, predicting protonation states of molecules, designing buffers, and drug development (affecting solubility and membrane permeability).

4. Using the Calculator

Tips: Enter pH value, concentrations of base and acid in mol/L. All values must be positive numbers. The concentrations should be from the same solution at equilibrium.

5. Frequently Asked Questions (FAQ)

Q1: What is the valid pH range for this calculation?
A: The equation is theoretically valid for pH values between 0-14, but practically most useful for pH values near the pKa (typically ±1 unit).

Q2: Can I use molarity or molality for concentrations?
A: The equation uses concentration ratios, so either molarity (mol/L) or molality (mol/kg) can be used as long as both [base] and [acid] use the same units.

Q3: Does temperature affect the calculation?
A: Temperature affects both pH measurements and pKa values, but the equation itself doesn't account for temperature. Measurements should be made at consistent temperatures.

Q4: What if my acid is polyprotic?
A: For polyprotic acids, each proton has its own pKa. This calculator assumes a simple monoprotic acid system.

Q5: How precise is this calculation?
A: The precision depends on the accuracy of your pH measurement and concentration determinations. The equation itself is mathematically exact for ideal solutions.