Blood as a Buffer

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Buffer solutions are extremely important in biology and medicine because most biological reactions and enzymes need very specific pH ranges in order to work properly.

Blood

Human blood contains a buffer of carbonic acid (\(\ce{H2CO3}\)) and bicarbonate anion (\(\ce{HCO3^{-}}\)) in order to maintain blood pH between 7.35 and 7.45, as a value higher than 7.8 or lower than 6.8 can lead to death. In this buffer, hydronium and bicarbonate anion are in equilibrium with carbonic acid. Furthermore, the carbonic acid in the first equilibrium can decompose into \(\ce{CO2}\) gas and water, resulting in a second equilibrium system between carbonic acid and water. Because \(\ce{O2}\) is an important component of the blood buffer, its regulation in the body, as well as that of \(\ce{O2}\), is extremely important. The effect of this can be important when the human body is subjected to strenuous conditions.

In the body, there exists another equilibrium between hydronium and oxygen which involves the binding ability of hemoglobin. An increase in hydronium causes this equilibrium to shift towards the oxygen side, thus releasing oxygen from hemoglobin molecules into the surrounding tissues/cells. This system continues during exercise, providing continuous oxygen to working tissues.

In summation, the blood buffer is:

\[\ce{H_3O^+ + HCO_3^- <=> H_2CO_3 + H_2O} \nonumber \]

With the following simultaneous equilibrium:

\[\ce{H_2CO_3 <=> H_2O + CO_2} \nonumber \]

Buffers are used often in biological research to maintain pH of specific processes. This can be especially useful when culturing bacteria, as their metabolic waste can affect the pH of their medium, consequently killing the sample. For example, a buffer of cacodylic acid (\(\ce{C2H7AsO2}\)) and its conjugate base is used to make samples which will undergo electron microscopy. Another buffer, tricine (\(\ce{C6H13NO5}\)), is used to buffer chloroplast reactions.

References

Brown, et al. Chemistry:The Central Science. 11th ed. Upper Saddle River, New Jersey: Pearson/Prentice Hall, 2008.
Chang, Raymond. General Chemistry:The Essential Concepts. 3rd ed. New York: Mcgraw Hill, 2003
Petrucci, et al. General Chemistry: Principles & Modern Applications. 9th ed. Upper Saddle River, New Jersey: Pearson/Prentice Hall, 2007.

Outside Links

Urbansky, Edward T.; Schock, Michael R. "Understanding, Deriving, and Computing Buffer Capacity." J. Chem. Educ. 2000 771640.