A buffer solution is a solution that resists significant changes in pH when small amounts of acid or base are added or when the solution is diluted.
Buffer solutions are essential for maintaining a stable pH in various biological systems, industrial processes, and analytical chemistry.
Types of buffer solutions:
1) Acidic buffer:
Contains a weak acid and its conjugate base (e.g., acetic acid and sodium acetate).
The weak acid neutralizes added base, and the conjugate base neutralizes added acid.
2) Basic buffer:
Contains a weak base and its conjugate acid (e.g., ammonia and ammonium chloride).
The weak base neutralizes added acid, and the conjugate acid neutralizes added base.
Properties of buffer solutions:
1) pH stability:
Buffers resist pH changes due to the presence of both a weak acid and its conjugate base (or weak base and its conjugate acid).
2) Optimal buffering range:
Buffers are most effective within one pH unit of the pKa (or pKb for bases) of the weak acid or base used.
3) Limited buffering capacity:
Buffers have a finite capacity. Once depleted, the buffer's pH changes more significantly upon further addition of acid or base.
Buffer equations:
1) Henderson-Hasselbalch Equation (for acidic buffers):
pH = pKa + log([A⁻]/[HA])
2) For basic buffers (in terms of pOH):
pOH = pKb + log([B]/[HB⁺])
Then, use pH + pOH = 14 (at 25°C) to find the pH
Buffer capacity:
A measure of a buffer's ability to resist pH changes upon adding acid or base.
β=dC/dpH
Maximum buffer capacity occurs when the concentrations of the weak acid/base and their conjugates are equal (pH = pKa or pOH = pKb).
Higher buffer component concentrations result in greater capacity to neutralize added acids or bases.