Ask A Scientist Chemistry Archive

Name         Cheryll
status       student
grade        9-12
location     CA

Question -   Does a buffer ALWAYS maintain a neutral pH?
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No. A buffer resists changes to whatever its pH was designed to be. The pH 
of the buffer can be set to a particular value depending on the pka of the 
weak acid used to make the buffer and the molarities of the weak acid and 
salt used. Look up the equation called: Henderson-Hasselbalch equation. 
This tells you the variables and how these variables control the pH of the 
buffer.

Greg (Roberto Gregorius)
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No. There are many buffers formulated to maintain a pH from the very
acidic to the very alkaline and all pH's in between. You can find the
various formulations in any analytical chemistry text or chemistry
handbooks. There are far too many to list here. For precision
measurements, pH meters are usually calibrated with a pH standard near
where the meter is going to be used in a particular experiment. Some
meters require standardization at 2 or 3 pH's if the use range is broad.
Often pH standards are available pre-made solutions or with packets to add
to a certain amount of distilled water. Check chemical suppliers for these
time savers.

Vince Calder
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Cheryll,

Buffers can be made for pH other than neutral, depending on the acid/base
being used.  Another thing that can happen is that acid (or base) added can
exceed the buffering capacity.

Don Yee
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Of course not.  It just adds some soggy inertia at its favorite pH.

A:  It can get used up by addition of excess acid or base, then the pH can 
change any distance in that direction.

B:  The change from active to "used up" is totally gradual.
       Any small addition of acid or base always changes the pH by a small 
 amount.
       If you learn the formula that governs it, you can calculate how much.
        The plateau at favored pH is slightly tilted at best,
        and curves away with increasing steepness on either side of 
 favored pH.

C:   Its favorite pH does not need to be "neutral" pH=7.
       There is a selection of standard buffers covering the center 80% of 
 the pH range of water.
       pH4 buffers (weakly acidic) are very commonly used, often for 
 keeping solution-electrodes preserved.
       For pH <1 or pH>13, buffers are less effective and the concept is 
 less meaningful.
       A solution concentrated to the point that ionization is not 
 complete, is the best one can do.

Jim Swenson
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No, the definition of a buffer is a substance that prevents a drastic  change
in the pH of a system.  Examples in biology are abundant.   Organisms are
adapted to the pH of their natural environment.  Higher  organisms even have
different areas of their bodies that have different  pH's.  For example, 
the pH of
the stomach of mammals is very acidic and  must stay that way to be able to
do its job.  However, the pH of the  intestines must be basic to 
counteract the
pH of the stomach contents.  The  pH of the blood and fluids should be a
little bit basic-7.4.  Buffers exist  to keep pH constant, not necessarily 
neutral.

vanhoeck
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