Buffer Solution
Definition and meaning of Buffer Solution in chemistry.
A buffer solution is a water based solution that resists big changes in pH. It contains a weak acid along with its conjugate base, or a weak base along with its conjugate acid. Both parts are present in similar amounts.
In more detail
When a small amount of acid is added to a buffer, the conjugate base part soaks it up. When a small amount of base is added, the weak acid part soaks it up instead. Because of this, the ratio between the two parts shifts only slightly, and the pH barely moves.
Buffering works best when the two components are present in roughly equal amounts. This happens when the solution's pH is close to the pKa. The pKa is a number that describes how strong the weak acid is.
A buffer eventually fails once one of its two parts runs out. It also fails if too much strong acid or base is added at once. This maximum capacity is called the buffer capacity.
It depends on how much weak acid and conjugate base are present in the solution. Buffers are essential for keeping pH steady in many settings. Biological fluids, like blood, depend on buffers to stay within a safe pH range.
Phosphate buffers are common inside living cells, helping control pH during many biochemical reactions. Laboratory reactions and many industrial processes also rely on buffers to keep conditions stable and predictable.
Key facts
| Field | General Chemistry |
|---|---|
| Key equation | Henderson-Hasselbalch, pH = pKa + log([A-] / [HA]) |
| Common lab example | CH3COOH and CH3COONa |
| Biological example | H2CO3 and HCO3- buffer blood near pH 7.4 |
| Works best | Within about one pH unit of the acid's pKa |
A mix of acetic acid and sodium acetate (CH3COOH and CH3COO-) buffers a solution near pH 4.74. Adding a little hydrochloric acid turns some acetate ions into acetic acid. Adding a little sodium hydroxide turns some acetic acid into acetate. In both cases, the pH shifts only a small amount.
Frequently asked questions
Why does a buffer resist pH change?
It contains a weak acid to soak up added base and a conjugate base to soak up added acid. This keeps the ratio between the two shifting only slightly, so the pH barely changes.
What is the effective pH range of a buffer?
A buffer works best within about one pH unit of its weak acid's pKa. Inside that range, both the acid and its conjugate base are present in large, similar amounts.
Can a buffer stop pH from changing forever?
No. A buffer can only absorb a limited amount of added acid or base. Once one of its two components runs out, further additions will change the pH sharply.