Overview
This lecture explains the concept of chemical buffers, how they resist pH changes when acids or bases are added, examples of buffer systems, and their significance in biological and environmental contexts.
Buffer Basics
- A buffer is a chemical system that resists changes in pH when small amounts of acid or base are added.
- Pure water’s pH changes rapidly with even small additions of acid or base, unlike buffers.
- Buffers act as "shock absorbers" for changes in acidity or basicity.
How Buffers Work
- A buffer typically consists of a weak acid and its conjugate base (or a weak base and its conjugate acid).
- When acid (H⁺) is added to a buffer, the conjugate base component binds the extra H⁺ ions, minimizing pH change.
- When base (OH⁻) is added, the weak acid component donates H⁺ ions to neutralize the OH⁻, stabilizing the pH.
- Le Chatelier’s principle explains buffer action: adding acid or base shifts the equilibrium to counteract the change.
Examples of Buffer Systems
- Acetic acid (weak acid) and sodium acetate (salt) form a common acidic buffer.
- Ammonia (weak base) and ammonium chloride (salt) create a basic buffer.
- Carbonic acid and sodium bicarbonate buffer system operates in the human body.
- Spectator ions like Na⁺ or Cl⁻ do not participate in buffer reactions.
Biological and Environmental Importance
- Proteins in living cells require a stable pH to function correctly; buffers protect cellular activity.
- The human body’s main buffer system uses carbonic acid and bicarbonate ions to maintain blood pH.
- Excess acid (e.g., from ethanol breakdown) can overwhelm buffers and harm the body.
- Soil buffers, such as humus particles, help stabilize soil pH and retain essential metal ions for plants.
- Acid rain can exceed soil buffering capacity, leading to nutrient loss and environmental harm.
Key Terms & Definitions
- Buffer — Solution that resists significant pH change upon addition of small amounts of acid or base.
- Weak acid/base — Partially dissociates in water, essential for buffer solutions.
- Conjugate base/acid — Species formed when an acid loses a proton or a base gains a proton.
- Spectator ion — Ion that does not participate in the buffer reaction.
- Le Chatelier’s Principle — When a system at equilibrium is disturbed, it shifts to counteract the change.
Action Items / Next Steps
- Review diagrams showing buffer reactions with added acid and base.
- Study examples of buffer systems.
- Read about environmental impacts of acid rain and soil buffering in your textbook.