What Does a Buffer Do in Chemistry?

Buffers are used in chemistry to modulate and stabilize the pH of a solution. A buffered solution can be made in a variety of ways, most simply by creating a mixture of a weak acid and its conjugate base.

History

Acids and bases play a central role in chemistry. The Bronsted theory of acids says that an acid is something that can donate a hydrogen, and a base is something that will accept a hydrogen. Common examples are acetic acid (found in vinegar) or sulfuric acid (found in car batteries).

Significance

An important number for any aqueous solution is its pH. The pH is the negative logarithm of the concentration of hydrogen ions (often represented as a hydronium ion, which is a water molecule with an extra proton attached). Anything with a pH of less than 7 is considered to be acidic, and a solution that has a pH of greater than 7 is basic. Pure water, which has an equal amount of acid and base in it, is defined as having a pH of 7.

Identification

Buffered solutions are used to make a solution that exhibits very little change in its pH when small amounts of an acid or base are added to it. A buffer can be made by addition of a weak acid and its conjugate base to a solution. Alternately, a weak base and its conjugate acid can be used. Buffers are most effective when the amounts of the weak acid/base and the conjugate base/acid are used---generally to be effective, neither quantity should be more than 10 times that of the other.

Features

The pH of a buffered solution is defined by the Henderson-Hasselbalch equation, which states that the pH of a solution is equal to the acid dissociation constant of the weak acid plus the logarithm of the ratio of the concentrations of conjugate base to the weak acid. The acid dissociation constant is a number that defines the tendency of an acid to dissociate and form hydrogen ions. A strong acid will have a very low dissociation constant, whereas a weaker one may have a significantly higher one, around 5.

Considerations

Buffered solutions have many applications in chemical manufacturing for processes that require a specific pH range to work. This is also true for the human body, which contains many enzymes that are only functional at a specific pH. Outside of this range, the enzymes are either unable to catalyze reactions, or in some case will misfold and become broken down; thus, a mixture of carbonic acid and bicarbonate is used by the body to keep pH of the blood between 7.35 and 7.45.