A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It has the property that the pH of the solution changes very little when a small amount of acid or base is added to it. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications.
The acid dissociation constant for a weak acid, HA, is defined as
The same considerations apply to a mixture of a weak base, B and its conjugate acid BH+.
In general a buffer solution may be made up of more than one weak acid and its conjugate base; if the individual buffer regions overlap a wider buffer region is created by mixing the two buffering agents.
Buffer capacity is a quantitative measure of the resistance of a buffer solution to pH change on addition of hydroxide ions. It can be defined as follows.
Buffer solutions are necessary to keep the correct pH for enzymes in many organisms to work. Many enzymes work only under very precise conditions; if the pH strays too far out of the margin, the enzymes slow or stop working and can denature, thus permanently disabling its catalytic activity. A buffer of carbonic acid (H2CO3) and bicarbonate (HCO3−) is present in blood plasma, to maintain a pH between 7.35 and 7.45.
Industrially, buffer solutions are used in fermentation processes and in setting the correct conditions for dyes used in colouring fabrics. They are also used in chemical analysis and calibration of pH meters.
|HCl, sodium citrate||1 - 5|
|citric acid, sodium citrate||2.5 - 5.6|
|acetic acid, sodium acetate||3.7 - 5.6|
|Na2HPO4, NaH2PO4||6 - 9|
|Borax, sodium hydroxide||9.2 - 11|
|0.2M Na2HPO4 /mL||0.1M Citric Acid /mL||pH|
|Common Name|| pKa|
|Buffer Range|| Temp Effect|
(pH / °C)**
|Full Compound Name|
** Values are approximate
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