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Buffer

Some Important Buffers

Common weak acid buffer systems are based upon carbonic acid (H2CO3), citric acid (H3C6H5O), and phosphoric acid (H3PO4). Common weak base buffer systems are based upon amines (organic bases) or amino acids, which can act as both acids and bases.

A buffer solution based upon a dibasic or tribasic acid (an acid that can produce two or three hydrogen ions per molecule) may be made from two different ions of the same acid, rather than from the acid itself and one salt ion. For example, the phosphoric acid ions H2PO- 4 and HPO2- 4 can form what is known as the phosphate buffer system, which is one of the buffers that control the pH of human blood. In this system the H2PO 4 ion plays the role of the weak acid and the HPO2- 4 ion plays the role of its salt. The relevant equilibrium is

The main buffer that is involved in controlling blood pH, however, is the carbonate system, which is based on the following equilibrium:

The carbonic acid in the blood comes from dissolved carbon dioxide:

Our breathing (oxygen in, carbon dioxide out) controls the amount of carbon dioxide that is available to dissolve in the bloodstream. Therefore, our lungs also play an important part in controlling our blood's pH through the carbonate buffer system.


Resources

Books

Brown, William H., and Elizabeth Rogers. General, Organic and Biochemistry. Boston: Willard Grant, 1980.

Creedy, John. A Laboratory Manual for Schools and Colleges. London: Heinemann, 1977.

Lide, D.R., ed. CRC Handbook of Chemistry and Physics. Boca Raton: CRC Press, 2001.

Ouellette, Robert. Chemistry: An Introduction to General, Organic, and Biological Chemistry. Prentice Hall, 1994.


Robert L. Wolke

KEY TERMS

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Amino acid

—An organic compound whose molecules contain both an amino group (-NH2) and a carboxyl group (-COOH). One of the building blocks of a protein.

Dissociate

—To break up into ions. Various compounds dissociate to various degrees when dissolved in water.

Electrolyte

—The chemical solution in which an electric current is carried by the movement and discharge of ions.

LeChâtelier's principle

—When a stress is applied to a system in equilibrium, the system shifts its balance (its amounts of reactants and products) in whichever direction partially relieves the stress.

pH

—A measure of the acidity of a solutionthat is, of the concentration of H+ ions in the solution. The pH is the logarithm of the molarity of H+ ions, with the sign changed.

Weak acid (base)

—An acid (base) that dissociates less than 100% into H+ (OH-) ions when dissolved in water. An acid (base) that is a weak electrolyte.

Additional topics

Science EncyclopediaScience & Philosophy: Boolean algebra to Calcium PropionateBuffer - Weak Acid Buffers, Weak Base Buffers, Some Important Buffers - How buffers work