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Name:  Cheryll
Status: student
Grade: 9-12
Location:CA
Country: N/A
Date: 8/28/2005


Question:
Does a buffer ALWAYS maintain a neutral pH?


Replies:
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)


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


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


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


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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