Stedman's > Henderson-Hasselbalch equation

Henderson-Hasselbalch equation

Pronunciation: hen′dĕr-sŏn hahs′ĕl-bawlk
a formula relating the pH value of a solution to the pK_a value of the acid in the solution and the ratio of the acid and the conjugate base concentrations: pH = pK_a + log([A−]/[HA]), where [A−] is the concentration of the conjugate base and [HA] is the concentration of the protonated acid. For the bicarbonate buffer system in blood, pH = pK′ + log([HCO₃−]/[CO₂]). The value of pK′ for blood plasma is 6.10 and includes the first dissociation constant of H₂CO₃, the relation between [H₂CO₃] and [CO₂], and other corrections. The partial pressure of CO₂ multiplied by its solubility in plasma at 38°C (0.0301 mM/mm Hg) is commonly substituted for [CO₂]; when the plasma bicarbonate concentration is 24 mEq/L and the P_CO2 is 40 mm Hg, the pH value is 6.10 + log(24/0.0301 × 40) = 7.40.

[Lawrence J. Henderson, Karl Hasselbalch]

 

 

 

 

 

 

 

 

 

 

 

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