biological chemistry

Titration Curve of a Weak Acid and its pKa (Biochemistry Notes)


Acetic Acid titration Curve

Titration Curve of a Weak Acid and its pKa
(Titration, Titration Curve, Titration Curve of Acetic Acid and its Significance)

What is Titration?

Titration is a method to determine the concentration of a dissolved substance (analyte or titrand) in a known volume by reacting it with another substance of known concentration and volume (titrant). The volume of the reactants plays a crucial role in the titration and thus the titration is better called as ‘volumetric analysis’.

There are different types of titrations in which the Acid-Base Titration is the most common one. The acid-base titration is used to determine the amount (concentration) of an acid in a given solution. In an acid-base titration, a known volume of acid (of unknown concentration) is titrated against a solution of strong base (usually NaOH) of known concentration in the presence of an indicator. After the titration, the concentration of the acid in the sample is calculated using the concept N1V1 = N2V2.

Where,

N1 – Normality of the unknown acid

N2 – Normality of the known base

V1 – Volume of unknown acid

V2 – Volume of the known base

What is Titration Curve?

The titration curve is a graphical representation of a titration in which the volume of titrant is plotted on X-axis (as the independent variable) and the pH of the solution is plotted on the Y-axis (as the dependent variable).

In simple terms, the titration curve is the plot of pH of the analyte (titrand) versus the volume of the titrant added as the titration progresses.

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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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