biological chemistry

pH and pKa – Henderson-Hasselbalch Equation Deriving


ph and pKa Relationship

Henderson–Hasselbalch Equation
How to Derive Henderson Hasselbalch Equation?

Henderson-Hasselbalch equation is a simple expression which relates the pH, pKa and the buffer action of a weak acid and its conjugate base. The Henderson-Hasselbalch equation also describes the characteristic shape of the titration curve of any weak acid such as acetic acid, phosphoric acid, or any amino acid. The titration curve of a weak acid helps to determine the buffering pH which is exhibited around the pKa of that acid. For example, in the case of acetate buffer, the pKa is 4.76. This is the best buffering pH of acetic acid. Besides, at this pH the acetic acid (CH3COOH) and acetate ions (CH3COO¯) will be at equimolar concentration in the solution. This equimolar solution of a weak acid and its conjugate base will resist the change in pH by donating or taking up the H⁺ ions. (pH is the negative logarithm of hydrogen ion concentration in a medium.The pKa is the negative logarithm of Ka. The Ka is the dissociation constant (similar to the equilibrium constant) for the ionization reaction of an acid.)

Learn more: Titration Curve of a Weak Acid (Acetic Acid)

In the present post, we will see the derivation of Henderson-Hasselbalch equation from the ionization reaction of a weak acid. We also discuss the significance of Henderson-Hasselbalch equation.

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