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What Is the Purpose of Buffers?

A buffer solution is used to resist changes in pH when a certain amount of strong acid or base is added to the solution. It is an important part of biological systems in living organisms as well as in the laboratory. The reason a buffer works to maintain a certain pH is that the concentration of weak acid and base is kept in a specific ratio in line with the acid titration curve.

  1. The titration curve

    • A titration curve is a graph that relates the relative concentrations of a weak acid to its conjugate base by graphing pH versus amount of base added. In the region of the titration curve where the graph is almost flat, the pH changes very little with added base and therefore this would be a good pH for the buffer.

    Buffer in cells and blood

    • The main buffer found in living cells is the H2PO4/HPO4- buffer pair. In blood, the main buffer is the H2CO3/HCO3- pair. This system relies on dissociation of carbonic acid, which has a pKa of 6.37. The pH of human blood needs to remain at around a pH of 7.4 and therefore the system also involves carbon dioxide transported to the lungs.

    Phosphate buffer

    • The phosphate buffer is based on tris (hydroxymethyl) aminomethane or TRIS. This buffer has a pKa of 8.3 and is found both in living organisms as well as used in the laboratory. It is a good buffer because it does not tend to interfere with the system being studied.

    Buffers in enzymatic reactions

    • Laboratory methods to isolate an enzyme use buffered solutions because an enzyme can only function in a narrow pH range. Enzymes are very sensitive to pH as well as salt concentrations. Therefore, it is important to use a buffer with a very good buffering capacity for the specific pH in order for the experiment to be successful.

    Physiological consequences

    • Respiration plays a role in buffering of blood by controlling the rate of respiration depending on the need for hydrogen ions or increased acidity. Increasing the rate of respiration is helpful when there is a buildup of hydrogen ions or acidity in the blood. The H+ ions bind to bicarbonate to form carbonic acid. This raises the level of carbon dioxide in the lungs. Increasing the level of respiration removes the excess carbon dioxide. Therefore, here the buffering system is used to keep pH level of the blood within the required narrow range.

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