Buffer capacity calculator explained
Buffer capacity tells you how many moles of strong acid or base are needed to shift a buffer's pH by one unit. This calculator tracks {amount_of_acid_base}, {initial_ph}, {final_ph}, and {buffer_capacity} so you can turn titration data into the value that compares different recipes objectively.
Use it while developing pharmaceutical buffers, validating bioreactor feeds, or teaching acid-base equilibrium so students see why buffers centered around values resist pH changes best.
How the conversion works
By definition,
where is the number of moles of strong acid or base added and . The calculator follows the IUPAC sign convention, so additions that lower pH produce negative values, but the magnitude of still represents resistance to change.
Units and conversions
| Quantity | Units | Notes |
|---|---|---|
| (buffer capacity) | mol per pH unit | Often reported as mol/L/pH when normalized by buffer volume. |
| mol | Convert from grams by dividing by molar mass. | |
| , | dimensionless | Measured before and after titrant addition. |
If you normalize by buffer volume, you obtain capacity per liter, which is useful when comparing batches of different sizes.
Worked examples
- Phosphate buffer challenged with acid
0.0020 mol HCl added to 0.100 L of phosphate buffer drops pH from 7.00 to 6.80 ().
Normalize by dividing by 0.100 L to report .
- Acetate buffer resisting base
Adding 0.00050 mol NaOH raises an acetate buffer from pH 4.75 to 4.90 ().
The lower capacity signals you should increase total buffer concentration if larger pH swings are expected.
Tips and pitfalls
- Keep pH increments small (\<0.2 units) when measuring so the Henderson-Hasselbalch approximation remains valid.
- Report whether the capacity was determined with acid or base; asymmetry appears near the buffer's limits.
- Temperature shifts change dissociation constants, so remeasure buffer capacity if the process temperature moves away from the calibration temperature.
- Combine this calculator with Henderson-Hasselbalch predictions to pick buffer ratios that deliver both the right pH and the needed capacity.