Buffer Solution
Definition and meaning of Buffer Solution in chemistry.
A buffer solution is an aqueous solution that resists large changes in pH when small amounts of acid or base are added, because it contains a weak acid together with its conjugate base (or a weak base together with its conjugate acid) at comparable concentrations.
In more detail
Added acid is consumed by the conjugate base component, while added base is consumed by the weak acid component, so the acid-to-conjugate-base ratio shifts only slightly rather than the hydrogen ion concentration changing sharply. Buffering is strongest when the two components are present in roughly equal amounts, which occurs when the solution pH equals the pKa of the weak acid, and it fails once one component is used up or an excess of strong acid or base is added. Buffers are essential for keeping pH stable in biological fluids, laboratory reactions, and industrial processes.
Key facts
| Field | General Chemistry |
|---|---|
| Key equation | Henderson-Hasselbalch: pH = pKa + log([A-]/[HA]) |
| Common lab example | CH3COOH / CH3COONa |
| Biological example | H2CO3 / HCO3- buffers blood at pH ~7.4 |
A solution of acetic acid and sodium acetate (CH3COOH/CH3COO-) buffers near pH 4.74; adding a little HCl converts some acetate ions to acetic acid, and adding a little NaOH converts some acetic acid to acetate, in both cases with only a small pH shift.
Frequently asked questions
Why does a buffer resist pH change?
Because it contains both a weak acid to neutralize added base and its conjugate base to neutralize added acid, so the ratio of the two shifts only modestly instead of the hydrogen ion concentration changing sharply.
What is the effective pH range of a buffer?
A buffer works best within about one pH unit of the pKa of its weak acid, the range over which both the acid and its conjugate base are present in significant, comparable amounts.