Buffer Preparation Calculator (Grams)
Work out how many grams of weak acid and conjugate base to weigh out to prepare a buffer at a target pH, total concentration and volume.
How it works
[A⁻]/[HA] = 10^(pH − pKa) · then grams = concentration × volume(L) × molar mass, split by that ratio
Preparing a buffer means dissolving a weak acid and its conjugate base in the exact proportion that fixes the pH. The Henderson–Hasselbalch equation gives the required base-to-acid ratio directly from the gap between the target pH and the acid’s pKa. Splitting the chosen total concentration into acid and base by that ratio, then multiplying each by the volume and its molar mass, tells you the grams to weigh for each component.
Worked example
For a 0.10 M, 1 L acetate buffer at pH 4.76 (pKa 4.76): the ratio is 10^0 = 1, so acid and base are equal at 0.05 M each. Grams of acetic acid = 0.05 × 1 × 60.05 = 3.00 g; grams of sodium acetate = 0.05 × 1 × 82.03 = 4.10 g.
Frequently asked questions
Should the target pH stay near the pKa?
Yes. A buffer works best within about one pH unit of the acid’s pKa, where neither component is nearly exhausted. Far outside that window the required ratio becomes extreme and buffering capacity collapses.
Can I use the acid plus a strong base instead of the salt?
Yes — dissolving the weak acid and neutralising part of it with NaOH generates the conjugate base in place. This calculator assumes you weigh out both the acid and its ready-made salt.
Why does the volume not change the pH?
pH depends only on the ratio of base to acid, not on their absolute amounts, so diluting the whole buffer leaves the pH essentially unchanged while lowering its capacity.
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This calculator is for educational purposes. Double-check important results before acting on them.