1. What is the Henderson-Hasselbalch Equation?

The Henderson-Hasselbalch equation relates the pH of a solution to the pKa of the acid and the ratio of the concentrations of the conjugate base ([A⁻]) and the acid ([HA]). It's particularly useful for buffer solutions and predicting the pH during titrations.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

Where:

• \( pH \) — The calculated pH of the solution
• \( pKa \) — The acid dissociation constant
• \( [A^-] \) — Concentration of conjugate base (mol/L)
• \( [HA] \) — Concentration of 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 the conjugate base and the acid.

3. Importance of pH Calculation

Details: Accurate pH calculation is crucial for preparing buffer solutions, understanding biological systems, and many chemical processes where pH control is essential.

4. Using the Calculator

Tips: Enter pKa value, concentrations of conjugate base and acid in mol/L. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: When is the Henderson-Hasselbalch equation valid?
A: The equation is valid when the concentrations of [A⁻] and [HA] are much greater than the concentration of H⁺ or OH⁻ ions in solution.

Q2: What are typical pKa values?
A: pKa values range from -10 for very strong acids to 50 for very weak acids. Common weak acids have pKa values between 2 and 12.

Q3: How does temperature affect the calculation?
A: The pKa value is temperature-dependent, so for precise calculations, use the pKa value at the appropriate temperature.

Q4: Can this be used for polyprotic acids?
A: For polyprotic acids, the equation can be applied to each dissociation step separately when the pKa values are sufficiently different.

Q5: What are common buffer systems?
A: Common buffers include acetate (pKa ≈ 4.76), phosphate (pKa ≈ 7.21), and Tris (pKa ≈ 8.07) buffer systems.