1. pH and Buffers

2. In solutions that are NOT buffered
When an acid is added: the pH decreases.
When a base is added: the pH increases.

3. A buffer allows an acid or base to be added to a solution without causing a major change in pH.
DOES NOT ALWAYS MAINTAIN IT AT NEUTRAL!
Stomach buffers keep the stomach at 2; blood buffers keep blood at
Buffers defined

4. A buffer solution contains a weak acid (HA) and its conjugate base (A-)
Both these components remain present in solution because they don’t undergo any reactions that significantly alter their concentration (they rarely react with water & when they react with themselves, the concentrations don’t change)
However, they will react with any excess H+ or OH- ions in solution.
Structure of a Buffer

5. Structure of a Buffer

6. A buffer works by soaking up (reacting with) any excess H+ or OH- depending on what was added. By reacting with the ions, a change in the pH of the system is prevented.
Generalized Summary

7. If a strong acid is added to a buffer, the weak base will react with the H+ from the strong acid to form the weak acid (HA):
H A-  HA
The H+ gets absorbed by the A- instead of reacting with water to form H3O+ (H+), so the pH changes only slightly.
Adding Acid to a Buffer

9. Adding a base to a buffer
When a strong base is added to a buffer, the weak acid (HA) will give up its H+ in order to transform the base (OH-) into water (H2O) and the conjugate base (A-):
HA + OH-  A- + H2O
Since the added OH- is consumed by the reaction, the pH will change only slightly
Adding a base to a buffer

11. The ratio of [A-]/[HA] influences the pH ; the actual concentrations of A- and HA influence the effectiveness of the buffer.
The more A- and HA available, the less of an effect the addition of acid or base will have on the pH. (The buffer will work longer).
Buffer Capacity