What defines the relationship between pH, pKa, and concentrations in the Henderson-Hasselbalch equation?

The correctness of the chosen answer is rooted in the proper formulation of the Henderson-Hasselbalch equation, which is crucial for understanding acid-base balance in physiological contexts. The equation describes the relationship between the pH of a solution, the pKa of a weak acid, and the concentrations of its dissociated (A-) and undissociated forms (HA).

In this case, the equation can be applied to the bicarbonate buffer system, where bicarbonate ion ([HCO3-]) acts as the base and carbon dioxide (CO2) represents the acid in equilibrium with carbonic acid (H2CO3). The correct form states that the pH is equal to the pKa plus the logarithm of the ratio of the concentration of bicarbonate to the partial pressure of carbon dioxide.

This relationship is significant because it shows how changes in the concentration of bicarbonate or the partial pressure of carbon dioxide affect the pH of blood, illustrating the principles of respiratory and metabolic disturbances. The inclusion of [HCO3-] over PCO2 accurately reflects the dynamic balance essential for maintaining acid-base homeostasis in the body.

Ultimately, the relationship encapsulated in this answer helps in diagnosing and understanding conditions related to acid-base im