1. What is the Henderson-Hasselbalch Equation?

The Henderson-Hasselbalch equation is used to estimate the pH of a buffer solution from the pKa of the acid and the concentrations of the acid and its conjugate base. It provides a simple way to calculate the pH of weak acid solutions.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

Where:

• \( pH \) — pH value (dimensionless)
• \( pKa \) — Acid dissociation constant (dimensionless)
• \( [\text{conjugate base}] \) — Concentration of conjugate base (mol/L)
• \( [\text{acid}] \) — Concentration of acid (mol/L)

Explanation: The equation relates the pH of a solution to the pKa of the acid and the ratio of the concentrations of the conjugate base to the acid.

3. Importance of pH Calculation in Buffer Solutions

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, conjugate base concentration, and acid concentration in mol/L. All concentration values must be positive numbers greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What is the valid range for the Henderson-Hasselbalch equation?
A: The equation works best when the concentrations of acid and conjugate base are within one order of magnitude of each other (0.1 < ratio < 10).

Q2: When is the Henderson-Hasselbalch equation not accurate?
A: The equation becomes less accurate for very dilute solutions, strong acids/bases, or when the ratio of [base]/[acid] is extremely large or small.

Q3: What are typical pKa values for common buffers?
A: Common biological buffers have pKa values around physiological pH (6-8), such as phosphate (pKa 7.2) and Tris (pKa 8.1).

Q4: Can this equation be used for polyprotic acids?
A: For polyprotic acids, the equation can be applied to each dissociation step separately, considering the appropriate pKa and concentrations.

Q5: Why is the logarithmic function used in this equation?
A: The log function converts the multiplicative relationship between concentrations into an additive relationship, making pH calculations linear with respect to concentration ratios.