By its nature, it does not take into account the self-dissociation of water, which becomes increasingly important in dilute solutions. However, this is not the problem most of the time. The resulting approximation breaks down in sufficiently dilute solution, and is already quite noticeable far before reaching water self-dissociation issues. So how can we visualize the effect of diluting a buffer without approximations, and where do the approximations start to break down? This can be done by titrating half of the weak acid with a strong monoprotic base e.
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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. 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. We also discuss the significance of Henderson-Hasselbalch equation. Deriving Henderson-Hasselbalch Equation 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.
Uses of 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.
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Henderson–Hasselbalch Equation: Derivation of pKa and pKb
What is Henderson-Hasselbalch Equation? (Basic Concept)