This assignment focuses on Biological Buffers II. There is also a description of Preparation of a Phosphate Buffer.An excellent example of buffer capacity is found in the blood plasma of mammals, which has a remarkably constant pH.
Biological Buffers II–Preparation of a Phosphate Buffer
When the concentrations of the conjugate acid and base of a buffering compound are equal, then pH = pKa. Also, this is the point of maximum buffering capacity of the solution. This is most obvious when a titration curve of the substance is generated by the titration of a buffer of a known concentration with varying amounts of a strong acid or base.
For a monoprotic buffer (i.e. made from a weak acid that contributes only a single proton, such as CH3COOH) the titration curve will look similar to that in Figure 3 but the volume of base required will vary depending on the initial concentration of the acid. For acids whose physical state is liquid in laboratory conditions, one must factor in their density (r = m/v) and, in some instances, their purity (if it is considerably lower than 100% v/v).
Biological Buffers II–Preparation of a Phosphate Buffer
An excellent example of buffer capacity is found in the blood plasma of mammals, which has a remarkably constant pH. Consider the results of an experiment that compares the addition of an aliquot of a strong acid to a volume of plasma with a similar addition of strong acid to either physiological saline (0.15 M NaCl) or water.
[1] Siegel IH (1976) Biochemical Calculations, 2nd Edition, John Wiley & Sons, pp. 83-86.
[2] Horton HR, Moran LA, Ochs RS, Rawn JD, Scrimgeour KG (2002) Principles of Biochemistry, 3rd edition, Prentice-Hall, Upper Saddle River, NJ, p. 41.
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