⚗ Aliquot

Buffer / pH

Henderson-Hasselbalch fixes the acid to base split for a target pH, then the total concentration sets the amounts.

Henderson-Hasselbalch

pH = pKa + lo g_{10} (\frac{[ A ^{-} ]}{[ HA ]})

\text{pH}	Target pH	dimensionless
\text{pKa}	Acid dissociation constant (log)	dimensionless
[\text{A}^-]	Conjugate base concentration	M
[\text{HA}]	Weak acid concentration	M

Tris pH 8.0 (pKa 8.06), 50 mM

For pH 8, combine 23.28 mM conjugate base with 26.72 mM acid.

Henderson-Hasselbalch equation

r = \frac{[ A ^{-} ]}{[ HA ]} = 1 0^{(pH - pKa)}

r	Base to acid ratio	dimensionless
\text{pH}	Target pH	dimensionless
\text{pKa}	Acid dissociation constant (log)	dimensionless

Henderson-Hasselbalch equation

[A^{-}] = C_{total} \cdot \frac{r}{1 + r}, [HA] = C_{total} \cdot \frac{1}{1 + r}

[\text{A}^-]	Conjugate base concentration	M
[\text{HA}]	Weak acid concentration	M
C_{\text{total}}	Total buffer concentration	M
r	Base to acid ratio	dimensionless

Henderson-Hasselbalch equation