Buffer
Definition and meaning of Buffer in chemistry.
A buffer is an aqueous solution consisting of a weak acid and its conjugate base, or a weak base and its conjugate acid, that resists significant changes in pH upon the addition of small amounts of strong acid or base. Buffers maintain a relatively stable hydrogen ion concentration by neutralizing added acidic or basic species.
In more detail
Buffer solutions function through the common ion effect and Le Chatelier's principle, shifting their chemical equilibrium to consume added H+ or OH- ions. The pH of a buffer is determined by the acid dissociation constant (pKa) of the weak acid and the ratio of the concentrations of the conjugate acid-base pair, as described by the Henderson-Hasselbalch equation. Effective buffering typically occurs within one pH unit of the weak acid's pKa. When a strong acid is introduced, the conjugate base component of the buffer reacts with the added hydrogen ions to form more weak acid, minimizing the drop in pH. Conversely, added hydroxide ions are neutralized by the weak acid component, generating more conjugate base and water. The overall buffering capacity depends on the absolute concentrations of the buffer components, with higher concentrations providing greater resistance to pH changes.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Key Equation | Henderson-Hasselbalch equation |
| Primary Components | Weak acid and conjugate base (or weak base and conjugate acid) |
| Optimal Range | pH = pKa +/- 1 |
| Function | Resists changes in hydrogen ion concentration |
The bicarbonate buffer system (H2CO3 / HCO3-) is the primary mechanism for maintaining blood pH in humans at a slightly basic level of 7.4.
Frequently asked questions
What determines the buffering capacity of a solution?
Buffering capacity is determined by the total concentrations of the weak acid and its conjugate base; higher concentrations can neutralize more added strong acid or strong base before a significant pH change occurs.
Can a strong acid and its salt act as a buffer?
No, a strong acid fully dissociates in water and cannot establish the necessary dynamic equilibrium with a conjugate base to neutralize added acids or bases effectively.