Why do buffer systems use either a weak acid or a weak base?
2 answers:
Answer:
Weak acids and weak bases are only partially dissociated.
Explanation:
When a small amount of an acid or a base is added to water (or a solution of some strong acid or base of some certain ,) the
of that solution tends to change significantly.
In contrast, when the same amount of acid or base is added to a buffer system of some certain , the
of this system tends to change by a much smaller amount.
Weak acids and weak bases dissociate only partially. That allows the buffer solutions to contain a large reservoir of both the (undissociated) weak acid (or weak base) and the corresponding conjugate ion, while maintaining the required .
This reservoir of the partially-dissociated weak acid (or weak base) and its conjugate ion allows the buffer system to absorb and
that were added to the solution without much change to the
.
For example, consider a buffer solution that initially included
of acetic acid
(a weak acid with
) and
of sodium acetate
. The
of this solution would be
.
In contrast, if a solution of (a strong acid) and an equal amount of
also needs to be
, only
of each species could be included.
Assume that of
is added to the buffer solution of
and
. The quantity of the partially-dissociated weak acid in this solution is much larger than that of the
added to the solution.
Only a small portion of the weak base would be consumed.The of the solution would likely change by less than
.
In contrast, assume that of
is added to the
solution with
of
(fully-dissociated) and
.
All the in this solution would be consumed. The
of this solution would go well above
.
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