Page 73 - Pharmaceutical_Analytical_Chemistry_1_Theoretical_Notes_Level_1

Mansoura National University
Pharm D-Clinical Pharmacy Program Level 1 Pharm. Anal. Chem. 1 (PC 101)

a. On addition of a strong acid to this buffer:

+ -
NH + H O  NH + OH
3 2 4 H O
+ 2
- + H
HCl → Cl + H
b. On addition of a strong base to this buffer:

+ -
NH + H O  NH + OH
3 2 4 -
OH
+ -
NaOH → Na + OH
Buffer Capacity

• The buffer capacity is a measure of the “strength” of the buffer, its ability
to resist changes in pH upon addition of a small amount of a strong

acid or a strong base.
• The greater the concentrations of the buffer components, the greater its
capacity to resist pH changes.
• The closer the component concentrations are to each other, the greater the
buffer capacity.
• The buffer has maximum capacity if the ratio "[ ]" /"[ ]" or

"[ ]" /"[ ]" = 1.

• Another quantitative definition of Buffer Capacity is as follows:

It is the number of moles of strong acid or strong base required to change pH of 1 liter

of the buffer solution by 1 pH unit.

Buffer Range

• The buffer range is the pH range over which the buffer is effective.
• Buffer range is related to the ratio of buffer component concentrations
• Buffers have a usable range within ± 1 pH unit of the pK of the acid
a
component.
The buffer range is the pH range over which the buffer is effective.

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