Page 71 - Pharmaceutical_Analytical_Chemistry_1_Theoretical_Notes_Level_1

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

- +
CH COOH  CH COO + H (slightly dissociated)
3 3

- +
CH COONa → CH COO + Na (highly dissociated)
3 3

Here, the acid will be less dissociated than if it was alone ( Why?)

• A solution containing both CH COOH and CH COONa will be less acidic
3 3

than a solution containing only CH COOH acid. WHY?
3
-
• According to Le Chȃtelier’s principle, the addition of CH COO ions from
3

CH COONa to a solution of CH COOH will suppress the ionization of
3 3
CH COOH acid (that is, shift the equilibrium from right to left). So,
3
+
decrease the (H ) ion concentration.

• According to Le Chȃtelier’s Principle:

(a) On addition of strong acid to this buffer:

- +
CH COOH  CH COO + H
3 3 +
- + H
HCl → Cl + H

(b) On addition of strong base to this buffer:

- + H O
CH COOH  CH COO + H 2
3 3 -
+ - OH
NaOH → Na + OH
• Equilibrium between acid and base.

• Example: Acetate buffer

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