بسم الله الرحمن الرحيم UMM AL-QURQ UNIVERSITY Faculty of Medicine Dep. Of BIOCHEMISTRY

Objectives: To prepare Buffer solutions. To show that the pH of buffer changes on dilution. To show that the buffer capacity varies with ionic strength.

 Buffer solution is a solution of conjugate acid/base pair that resists changes in pH as a result of dilution or the addition of small amount of strong acid or base.  It can be prepared either by mixing weak acid with its conjugate base (salt), or by adding small amount of strong base to weak acid or by adding small amount of strong acid to weak base. Buffer solutions

 Buffers are used in experiments or applications whenever the pH of a solution is needed to be maintained constant or at a predetermined level.  Note in Figure how the plot of pH versus base added is flat near the pK a.  Buffers can only be used reliably within a pH unit of their pK a.

What are the unique properties of buffer solution? Buffers do not maintain pH at absolutely constant value, but changes in pH are relatively small when amounts of acids or bases are added. 1.Effect of dilution 2.The effect of added acids and bases 3.The buffer capacity, (what is buffer capacity?)

Calculating the pH of Buffer solutions

What is the pH of a solution that is 0.4 M in formic acid and 1.0 M of sodium formate. (K a, HCOOH = 1.8 x ) Example:

ABDULLATIF TAHA ABDULLA MSc. BIOCHEMISTRY