Buffers
a buffer is a solution that is resistant to changes in pH
What does a BUFFER do?
- sometimes it is desirable to keep a fairly constant pH while acids or bases are added to the solution either by a reaction or by the experimenter, and buffers are designed to fill that role
- buffers are used routinely to moderate the pH of a reaction
- in medicine buffers are sometimes used to control blood pH or used to ensure that urine does not reach painfully acidic levels
- a buffer is a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid, and they work by reacting with any added acid or base to control the pH
Examples of Buffers
consider the action of a buffer composed of the weak base ammonia, NH3, and its conjugate acid, NH4+
- when HCl is added to that buffer, the NH3 "soaks up" the acid's proton to become NH4+
- since that proton is locked up in the ammonium ion, its proton does not serve to significantly increase the pH of the solution
- when NaOH is added to the same buffer, the ammonium ion donates a proton to the base to become ammonia and water (here the buffer also serves to neutralize the base)
- as the above example and picture show, a buffer works by replacing a strong acid or base with a weak one
- in this case the strong acid's proton is replaced by an ammonium ion (a weak acid) and the strong base OH- was replaced by the weak base ammonia
- replacements of strong acids and bases for weaker ones give buffers their extraordinary ability to moderate pH
Done with buffers?