Acid Buffer Solution

BUFFERS

By: Luis P. Bazan, RPh., Ph.D.

A buffer solution is a solution of:
1. A weak acid or a weak base and
2. The salt of the weak acid or weak base

Both must be present!
A buffer solution has the ability to resist changes in pH upon the addition of small amounts of either acid or base.
Consider an equal molar mixture of CH3COOH and CH3COONa
CH3COOH (aq)

H+ (aq) + CH3COO- (aq)

Adding more acid creates a shift left IF enough acetate ions are present

16.3

Which of the following are buffer systems?
(a) KF/HF
(b) KCl/HCl,
c) Na2CO3/NaHCO3

(a) KF is a weak acid and F- is its conjugate base buffer solution
(b) HCl is a strong acid not a buffer solution
(c) CO32- is a weak base and HCO3- is it conjugate acid buffer solution

16.3

Buffers
• are solutions that have the property of resisting changes in pH when acids or bases are added to them
• this property results from the presence of a buffer pair which consists of either:
 weak acid and some salt of a weak acid/its conjugate base
Ex. Acetic acid and sodium acetate
 weak base and some salt of a weak base/its conjugate acid
Ex. Ammonium hydroxide and ammonium chloride

BUFFERS IN BIOLOGIC SYSTEMS
 Blood is maintained at a pH about 7.4 by the so-called primary buffers in the plasma and the secondary buffers in the erythrocytes.  The plasma contains carbonic acid/bicarbonate and acid/alkali sodium salts of phosphoric acid as buffers
 Plasma proteins, which behaves as acids in blood can combine with bases and so act as buffers.
 In the erythrocytes, the two buffer systems consist of hemoglobin/oxyhemoglobin and acid/alkali potassium salts of phosphoric acid.

Pharmaceutical Applications
(1) Preparation of such dosage forms as injections and ophthalmic solutions which are placed directly into pH-sensitive body fluids (2) Manufacture of formulations in which the pH must be maintained at a relatively constant level to ensure maximum product