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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.
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