Question

From the Henderson-Hasselbalch equation, explain how the ratio [Al/[HA] changes with changing pH

Answer 1

Answer:

The ratio [A-]/[HA] increase when the pH increase and the ratio decrease when the pH decrease.

Explanation:

Every weak acid or base is at equilibrium with its conjugate base or acid respectively when it is dissolved in water.

$HA + H_{2}O$ ⇄ $A^{-} + H_{3}O^{+}$

This equilibrium depends on the molecule and it acidic constant (Ka). The Henderson-Hasselbalch equation,

$pH = pKa + Log \frac{[A^{-}]}{[HA]}$

shows the dependency between the pH of the solution, the pKa and the concentration of the species. If the pH decreases the concentration of protons will increase and the ratio between A- and AH will decrease. Instead, if the pH increases the concentration of protons will decreases and the ratio between A- and AH will increase.