Deriving Henderson-Hasselbalch Equation Step by Step. The Relationship between pH, pKa, Titration Curve and Buffer Action of a Weak Acid. The Significance. Derivation of the Henderson –Hasselbalch Equation for weak base. B + HOH. BH . +. + OH. – or. B. –. + HOH. BH + OH. –. Either one works, but you have to be. Henderson–Hasselbalch equation describes the derivation of pH as a measure of acidity using the acid dissociation constant (pKa.

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Henderson-Hasselbalch equation is a simple expression which relates the pHpKa 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.


Deriving the Henderson-Hasselbach Equation

For example, in the case of acetate buffer, the pKa is 4. This is the best buffering pH of acetic acid.

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

How to Derive Henderson Hasselbalch Equation | easybiologyclass

We also discuss the significance of Henderson-Hasselbalch derivatioon. Take the ionization reaction of a weak acid HA: The dissociation constant Ka of the above reaction will be: Dissociation constant is the ratio of the concentration of products by the concentration of reactants. Then take the negative logarithm of both sides: Substitute the pH and pKa in the equation 4: Thus the equation 6 can be better stated as: The above equation is called the Henderson-Hasselbalch equation.

The Henderson—Hasselbalch is mainly used for calculating the pH or pKa of a solution containing known quantities of a weak acid and its conjugate base. We have already stated that for a buffer the best buffering pH is at its pKa.


Also remember, the buffer is a mixture of equimolar concentration of weak acid and its conjugate base. This also proved that for a buffer, the best buffering activity is obtained at the pH value equal to its pKa value. You might also like…. Titration Curve hasselbalcg Weak Acid.


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