Henderson-Hasselbalch Calculator

Your details

Choose which unknown you want to find. The other two fields become your inputs. Solving for ratio tells you how to mix the buffer; solving for pKa lets you identify an unknown acid.
Acid buffers use pH = pKa + log([A⁻]/[HA]). Base buffers work in terms of pOH = pKb + log([BH⁺]/[B]) and then pH = 14 - pOH (at 25 °C).
Select a common acid to auto-fill the pKa. Choose "Custom" to type in your own pKa.
The negative log of the acid dissociation constant. Auto-filled when you pick a preset above. Range is typically 2 to 12 for common buffer acids.
Molar concentration of the deprotonated (conjugate-base) species. Must be greater than zero. For a base buffer this is the neutral weak-base form [B].
mol/L
Molar concentration of the protonated (acid) species. Must be greater than zero. For a base buffer this is the conjugate-acid form [BH⁺].
mol/L
Buffer pHAcidic
4.76
pOH9.24
[A⁻]/[HA] ratio1
pKa (derived)4.76
Conjugate base fraction50%
Effective buffer range3.76 - 5.76
4.76 pH
Strong acid<3Acidic3-6Near-neutral6-8Basic8-11Strong base11+

This buffer holds pH 4.76.

  • Buffer pH is 4.76, giving a pOH of 9.24 at 25 °C.
  • The base-to-acid ratio is 1, meaning the solution is 50% in the conjugate-base form.
  • The pH is within 1 unit of the pKa (4.76), so this buffer is in its most effective operating range.
  • Because only the ratio matters, diluting the buffer barely shifts its pH, but it does reduce the buffer capacity.

Next stepTo maximise buffering power, choose an acid with a pKa within ±1 pH unit of your target and keep the base-to-acid ratio between 0.1 and 10.

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