Can I use mM or mol/L?

Yes. Use the same unit for acid and base; the ratio controls pH.

Does this include activity or temperature corrections?

No. It is a Henderson-Hasselbalch estimate for routine buffer planning.

Calculate buffer pH, base/acid ratio, and the recipe ratio for a target pH.

Answer

7.297

Buffer pH

Base / acid ratio: 1.25

Target base / acid ratio: 1.585

pH - pKa: 0.097

Buffer range: Within pKa +/- 1

pKaConjugate base [A-] (mM)Weak acid [HA] (mM)Target pHTarget total buffer (mM)

Examples

Recipe summary

	Acid fraction	Base fraction	Base / acid ratio
Current mixture	44.444%	55.556%	1.25
Target pH recipe	Target acid: 19.343 mM	Target base: 30.657 mM	1.585

pH = pKa + log10([A-]/[HA])

The Henderson-Hasselbalch equation estimates buffer pH from the conjugate base to weak acid ratio.

Symbol	Variable	Description
pKa	Acid dissociation value	The pH where acid and base forms are equal.
[A-]	Conjugate base	Base form concentration.
[HA]	Weak acid	Acid form concentration.

Buffers usually work best within about one pH unit of pKa.

pH - pKa	Typical use
-1 to +1	Good buffer range
Outside +/- 1	Buffer capacity is weaker

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