What is the Henderson-Hasselbalch equation primarily used for?

The Henderson-Hasselbalch equation is primarily used for determining the pH of a solution based on the concentrations of a weak acid and its conjugate base. The equation is expressed as:

[ \text{pH} = \text{p}K_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) ]

where ( \text{p}K_a ) is the negative logarithm of the acid dissociation constant. This relationship shows how the pH of a buffer solution is influenced by the ratio of the concentrations of the weak acid (HA) to its conjugate base (A−).

In the context of buffer solutions, which resist changes in pH upon the addition of acids or bases, this equation is essential for predicting how the pH will change based on the relative amounts of the weak acid and conjugate base present. It is particularly useful in biochemical and physiological applications where maintaining a stable pH is critical.

The other options do not accurately represent the function of the Henderson-Hasselbalch equation. For instance, calculating the pH at the equivalence point pertains to titration scenarios, which involve strong acids and bases