Henderson-Hasselbalch Calculator
Calculate pH, pKa, and concentrations using the Henderson-Hasselbalch equation for buffer solutions
Henderson-Hasselbalch Equation
Molar concentration of the conjugate base
Molar concentration of the weak acid
Negative logarithm of acid dissociation constant
Calculation Results
Example Calculation
Acetate Buffer Example
Buffer System: Acetic acid (CH₃COOH) / Acetate (CH₃COO⁻)
pKa of acetic acid: 4.76
Concentration of CH₃COOH: 0.1 M
Concentration of CH₃COO⁻: 0.15 M
Henderson-Hasselbalch Calculation
pH = pKa + log([A⁻]/[HA])
pH = 4.76 + log(0.15/0.1)
pH = 4.76 + log(1.5)
pH = 4.76 + 0.176
pH = 4.94
Common Buffer Systems
Acetate Buffer
Formula: CH₃COOH/CH₃COO⁻
pKa: 4.76
Range: 3.8 - 5.8
Phosphate Buffer
Formula: H₂PO₄⁻/HPO₄²⁻
pKa: 7.21
Range: 6.2 - 8.2
Tris Buffer
Formula: Tris-H⁺/Tris
pKa: 8.06
Range: 7.1 - 9.1
HEPES Buffer
Formula: HEPES-H⁺/HEPES
pKa: 7.55
Range: 6.8 - 8.3
Bicarbonate Buffer
Formula: H₂CO₃/HCO₃⁻
pKa: 6.37
Range: 5.4 - 7.4
Imidazole Buffer
Formula: Im-H⁺/Im
pKa: 7
Range: 6.2 - 7.8
Henderson-Hasselbalch Tips
Best buffering occurs at pH = pKa
Effective range: pKa ± 1 pH unit
Equal concentrations give pH = pKa
Higher ratio [A⁻]/[HA] = higher pH
pKa = -log₁₀(Ka)
Understanding the Henderson-Hasselbalch Equation
What is the Henderson-Hasselbalch Equation?
The Henderson-Hasselbalch equation relates the pH of a buffer solution to the pKa of the weak acid and the ratio of concentrations of the conjugate base and weak acid. It's fundamental for understanding acid-base equilibria and buffer systems.
Applications
- •Buffer solution preparation
- •Physiological pH regulation (blood, etc.)
- •Protein and enzyme studies
- •Analytical chemistry and titrations
The Equation
pH = pKa + log([A⁻]/[HA])
- pH: Negative logarithm of hydrogen ion concentration
- pKa: Negative logarithm of acid dissociation constant
- [A⁻]: Concentration of conjugate base
- [HA]: Concentration of weak acid
Key Relationships
- When [A⁻] = [HA]: pH = pKa
- When [A⁻] > [HA]: pH > pKa (more basic)
- When [A⁻] < [HA]: pH < pKa (more acidic)
Remember: The equation assumes ideal solutions and constant ionic strength. For precise work, activity coefficients may be needed.