HendersonHasselbalchi

Henderson-Hasselbalch equation is a mathematical expression used to calculate the pH of a buffer solution. It is named after Lawrence Joseph Henderson and Karl Albert Hasselbalch, who independently derived the equation in the early 20th century. The equation is derived from the definition of pH and the equilibrium expression for a weak acid and its conjugate base.

The Henderson-Hasselbalch equation is expressed as:

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

where pH is the negative logarithm of the hydrogen ion concentration, pKa is the negative logarithm of the acid dissociation constant, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the weak acid.

The equation is particularly useful in biochemistry and medicine, where it is used to determine the pH of blood and other bodily fluids. It is also used in the design and analysis of buffer solutions, which are solutions that resist changes in pH when small amounts of acid or base are added.

The Henderson-Hasselbalch equation assumes that the concentration of the weak acid and its conjugate base are much greater than the concentration of the hydrogen ion, which is a reasonable assumption for most buffer solutions. It also assumes that the activity coefficients of the weak acid and its conjugate base are equal, which is a good approximation for dilute solutions.

In summary, the Henderson-Hasselbalch equation is a powerful tool for calculating the pH of buffer solutions and understanding the behavior of weak acids and their conjugate bases. It has numerous applications in chemistry, biochemistry, and medicine.