1. Buffered Solutions
- A solution that can resist a change in pH when an acid, H+, or base, OH-, is added

2. Typical Buffers Usually acid/c.base or c.acid/base
Examples: HC2H3O2/NaC2H3O2 or NH4Cl/NH3
Buffers can be made to achieve any pH.

3. HC2H3O2 (aq)  H+ (aq) + C2H3O2 1- (aq)
Calculate the pH of a 0.50 M HC2H3O2/0.50 M NaC2H3O2 solution. Ka = 1.8 x 10 -5
Major species:
HC2H3O2 (aq)  H+ (aq) + C2H3O2 1- (aq)
I M M
C X +X X
E – X X X
Assume X’s = 0, and solve
Notice when the [acid]=[base], then pH = pKa
HC2H3O2, Na+, C2H3O2 1-, H2O
= 1.8 x 10 -5

4. Buffers made easy Henderson-Hasselbalch equation
Used for buffer solutions
Same problem
= 4.74

5. Now with the addition 0.010 mol NaOH to 1 L of 0.50 M HC2H3O2/NaC2H3O2
ms: HC2H3O2, Na+, OH-, C2H3O2 1-, H2O
Mixing an acid, HC2H3O2, with OH-
HC2H3O2 (aq) + OH-  C2H3O2 1- (aq) + H2O (l)
I.C.E. must be in MOLES
I mol mol mol C E
= log(.51/.49) = 4.76