Henderson-Hasselbalch (Buffer pH)
pH = pKa + log([A⁻]/[HA]). Predict buffer pH from acid + conjugate base concentrations.
Result
pH
4.7600
[A⁻]/[HA] = 1.0000. Optimal buffer (within 1 pH of pKa).
- pKa4.76
- [A⁻]0.1 M
- [HA]0.1 M
- [A⁻]/[HA]1.000000
- log([A⁻]/[HA])0.0000
- pH4.760000
Step-by-step
- pH = pKa + log([A⁻]/[HA]).
- = 4.76 + log(0.1/0.1) = 4.76 + 0.0000 = 4.7600.
How to use this calculator
- Enter pKa of weak acid.
- Enter [A⁻] and [HA].
- Read pH.
About this calculator
Henderson-Hasselbalch: pH = pKa + log([A⁻]/[HA]). When [A⁻] = [HA], pH = pKa exactly. A buffer's "optimal" range is pH = pKa ± 1 (ratio 1:10 to 10:1). Below or above, buffering capacity drops dramatically. Used in biology (blood ~7.4, buffered by carbonate), pharmaceuticals (drug formulation), brewing, and pool chemistry.
Frequently asked
Weak acid + conjugate base buffer. Strong acids/bases need ICE tables. Approximation valid when both [A⁻] and [HA] >> [H⁺] (works for >0.001 M typically).
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