1. What Is The Henderson-Hasselbalch Equation?

The Henderson-Hasselbalch equation is used to estimate the pH of buffer solutions. It relates the pH, pKa (acid dissociation constant), and the ratio of 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:

Where:

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

Explanation: When the concentrations of conjugate base and weak acid are equal (0.01 M each), the log term becomes zero and pH equals pKa.

3. Importance Of pH Calculation For Buffer Solutions

Details: Accurate pH calculation is crucial for understanding buffer capacity, predicting how a buffer will respond to added acid or base, and designing effective buffer systems for biological and chemical applications.

4. Using The Calculator

Tips: Enter pKa value, conjugate base concentration, and weak acid concentration in mol/L. All concentrations must be positive values. For equal 0.01 M concentrations, pH will equal pKa.

5. Frequently Asked Questions (FAQ)

Q1: What happens when [A⁻] = [HA]?
A: When the concentrations are equal, the log term becomes log(1) = 0, so pH = pKa.

Q2: What are typical pKa values for common buffers?
A: Common buffers include acetic acid (pKa = 4.76), phosphate (pKa = 7.2), and Tris (pKa = 8.06).

Q3: What is the effective buffer range?
A: Buffers are most effective when pH is within ±1 unit of the pKa value (pH = pKa ± 1).

Q4: Are there limitations to this equation?
A: The equation assumes ideal behavior and may be less accurate for very concentrated solutions or when activity coefficients differ significantly from 1.

Q5: Can this calculator be used for polyprotic acids?
A: For polyprotic acids, each dissociation step has its own pKa and should be considered separately based on the pH range.