Definition: A buffer is a solution that can resist changes in pH when small amounts of an acid or a base are added.
Components: Typically made of a weak acid and its conjugate base, or a weak base and its conjugate acid.
How Buffers Work
Resistance to pH Change: Buffers work by neutralizing added acids or bases.
Mechanism:
Acid Added: The conjugate base in the buffer solution will neutralize the added acid.
Base Added: The weak acid in the buffer solution will neutralize the added base.
Dynamic Equilibrium: Buffers maintain a stable pH by constantly adjusting the equilibrium between the weak acid and its conjugate base.
Composition of Buffers
Weak Acid and Conjugate Base Pair: For example, acetic acid (CH₃COOH) and sodium acetate (CH₃COONa).
Weak Base and Conjugate Acid Pair: For example, ammonia (NH₃) and ammonium chloride (NH₄Cl).
Henderson-Hasselbalch Equation
Purpose: Used to calculate the pH of buffer solutions.
For Acid Buffers:pH=pKa+log([HA][A−]), where[A−] is the concentration of the conjugate base and[HA] is the concentration of the acid.
For Base Buffers: Similar formula, but withpKb and the concentrations of the weak base and its conjugate acid.
Creating a Buffer
Choosing Components: Select a weak acid/base whose pKa or pKb is close to the desired pH.
Ratio: Adjust the ratio of acid to conjugate base (or base to conjugate acid) to achieve the desired pH.
Limitations of Buffers
Capacity: Buffers have a limited capacity to neutralize acids or bases. Once exceeded, the pH will change more rapidly.
Concentration Dependent: The effectiveness of a buffer depends on the concentrations of its components.
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