Equilibrium plays a key role in buffer solutions, which are used to maintain a stable pH.
- Buffer composition:
- A buffer usually contains a weak acid and its salt (conjugate base) or a weak base and its salt (conjugate acid).
- How it resists pH changes:
- When acid is added: The conjugate base reacts with the added hydrogen ions to form the weak acid, shifting the equilibrium slightly but keeping pH nearly constant.
- When base is added: The weak acid reacts with the added hydroxide ions to form its conjugate base, again shifting the equilibrium to minimize pH change.
- Dynamic balance:
- The acid and conjugate base are in dynamic equilibrium, constantly adjusting to neutralize added acids or bases.
In short: Buffers use chemical equilibrium to resist changes in pH by adjusting the balance between weak acids and their conjugate bases (or weak bases and their conjugate acids).