Buffer Recipe Calculator
Calculate the required concentrations and molar amounts of weak acid and conjugate base components using the Henderson-Hasselbalch equation.
Buffer System Properties
Specify acid pKa, target pH, concentration, and volume.
Required Base / Acid Ratio
* Ratio of [conjugate base] to [weak acid].
Effective Range
Buffers work best when target pH is within ±1 unit of pKa. Outside this range, buffer capacity is rapidly exhausted.
Common Biological Buffers & pKa Values Reference Table
| Buffer System | pKₐ (at 25°C) | Effective pH Range | Primary Application |
|---|---|---|---|
| Acetate Buffer | 4.76 | 3.8 – 5.8 | Enzyme kinetics, protein precipitation |
| Phosphate (PBS) pKa2 | 7.20 | 6.2 – 8.2 | Physiological cell culture, immunology |
| Tris Buffer | 8.06 | 7.0 – 9.0 | DNA/RNA biochemistry, PAGE electrophoresis |
| HEPES Buffer | 7.48 | 6.8 – 8.2 | Good's buffer for cell culture media |
Methodology & Equations
Henderson-Hasselbalch
Calculates the logarithmic ratio of conjugate base ($[A^-]$) to weak acid ($[HA]$).
Stoichiometric Split
Splits total concentration C based on ratio R = 10^(pH - pKa).
Frequently Asked Questions
What is the Henderson-Hasselbalch equation? ▼
The Henderson-Hasselbalch equation is pH = pKa + log10([Base] / [Acid]). It calculates the required ratio of conjugate base ([A⁻]) to weak acid ([HA]) for a buffer solution at a given pH.
What is optimal buffer capacity? ▼
Buffer capacity is highest when the target pH equals the acid's pKa (where [Base] = [Acid]). In ptice, effective buffer capacity spans pKa ± 1 pH unit.
Why should temperature be considered when preparing biological buffers? ▼
The pKa of amine buffers like Tris decreases as temperature rises (-0.031 pH units/°C). A Tris buffer prepared at pH 8.0 at 25°C will shift to ~pH 8.6 at 4°C.