0.0387
M
0.0613
M
0.038686
mol
0.061314
mol
1.5849
0.3869
0.6131
0.1
mol
0.0387
M
0.0613
M
0.038686
mol
0.061314
mol
1.5849
0.3869
0.6131
0.1
mol
The Buffer Preparation Calculator determines the amounts of weak acid and conjugate base needed to prepare a buffer solution at a specific pH. Using the Henderson-Hasselbalch equation in reverse, it calculates the required ratio and then the individual concentrations and moles for your desired volume.
Enter your target pH, the pKa of the buffer acid, the total buffer concentration, and the desired final volume. The calculator outputs the concentrations and moles of both the acid and conjugate base components, making it straightforward to weigh out reagents for buffer preparation.
Starting from the Henderson-Hasselbalch equation:
pH = pKa + log10([A⁻]/[HA])
The ratio of conjugate base to acid is:
[A⁻]/[HA] = 10^(pH - pKa)
Since the total concentration C = [A⁻] + [HA], we can solve:
[A⁻] = C x ratio / (1 + ratio)
[HA] = C x 1 / (1 + ratio)
Moles are then obtained by multiplying each concentration by the volume in liters. This approach works for any buffer system where you know the pKa.
Inputs
Results
For 1 L of 0.1 M phosphate buffer at pH 7.0 (pKa = 6.80), use approximately 0.0613 M Na2HPO4 and 0.0387 M NaH2PO4.
Inputs
Results
For 500 mL of 0.05 M acetate buffer at pH 5.0, you need about 0.0142 mol sodium acetate and 0.0108 mol acetic acid.
Choose a buffer whose pKa is within 1 pH unit of your target pH. Common biological buffers include acetate (pKa 4.76), MES (pKa 6.15), phosphate (pKa 6.80), HEPES (pKa 7.48), Tris (pKa 8.06), and CHES (pKa 9.50). The buffer will have maximum capacity when the target pH equals the pKa.
The total buffer concentration is the sum of the weak acid and conjugate base concentrations: C = [HA] + [A⁻]. Higher total concentrations provide greater buffer capacity. Typical biological buffers range from 10 mM to 100 mM. Very high concentrations can affect ionic strength and enzyme activity.
Yes. After dissolving the calculated amounts of acid and base in most of the final volume, measure the pH with a calibrated pH meter and make small adjustments with concentrated acid or base. Then bring to the final volume. Temperature affects pH, so measure at the temperature the buffer will be used.
Roboculator Team
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