Buffer action capacity

FIGURE 2.15 A buffer system consists of a weak acid, HA, and its conjugate base, A. The pH varies only slightly in the region of the titration curve where [HA] = [A ]. The unshaded box denotes this area of greatest buffering capacity. Buffer action when HA and A are both available in sufficient concentration, the solution can absorb input of either H or OH, and pH is maintained essentially constant. 

Buffer action 46 Buffer capacity 48 Buffer mixture universal, (T) 831 Buffer solutions 46, (T) 831 acetic acid-sodium acetate, 49 for EDTA titrations, 329 preparation of IUPAC standards, 569 Bumping of solutions 101 Buoyancy of air in weighing 77 Burette 84, 257 piston, 87 reader, 85 weight, 86... 

Solutions in which the buffering action is due to the solvent rather than any added solute Strongly acidic or basic aqueous solutions will show httle change in pH when additional increments of acid or base are added (recall that the pK value for H3O+ is -1.74, and that for H2O is 15.74) . Because the solvent is in such high concentration, the buffering capacity for pseudo buffers is larger than for conventional buffers. See Buffer Capacity... 

Mixed Solutions and Buffers 11.1 Mixed Solutions 1 1.2 Buffer Action 11.3 Designing a Buffer 1 1.4 Buffer Capacity... 

Just as a sponge can hold only so much water, a buffer can also run out of mopping-up power. Its proton sources and sinks become exhausted if too much strong acid or base is added to the solution. Buffer capacity is the amount of acid or base that can be added before the buffer loses its ability to resist the change in pH. A buffer with a high capacity can maintain its buffering action longer than can one with only a small capacity. 

Bassam Z. Shakhashiri, "Buffering Action and Capacity," Chemical Demonstrations, A Handbook for Teachers of Chemistry, Vol. 3 (The University of Wisconsin Press, Madison, 1989) pp. 173-185. 

Buffering action appears to help determine the sourness of various acids this may explain why weak organic acids taste more sour than mineral acids of the same pH. It is suggested that the buffering capacity of saliva may play a role, and foods contain many substances that could have a buffering capacity. 

B. The side chains of the amino acid residues in proteins contain functional groups with different pKs. Therefore, they can donate and accept protons at various pH values and act as buffers over a broad pH spectrum. There is only one N-terminal amino group (pK=9) and one C-terminal carboxyl group (pK= 3) per polypeptide chain. Peptide bonds are not readily hydrolyzed, and such hydrolysis would not provide buffering action. Hydrogen bonds have no buffering capacity. 

The choice of buffer to use in a given situation therefore depends on the pXa of the acid or base involved. As a general rule, buffer solutions work well within plus or minus one pH unit of the pKa. Beyond these values, the buffer capacity is too small to allow effective buffer action. 

Not all mixtures of a weak acid with its salt have the same buffer capacity or intensity. The best buffer action is displayed at the hydrogen ion concentration of the half-neutralized acid. 

We can measure buffer action in terms of a definite unit called buffer capacity or buffer index x, where... 

In Fig. 4 is shown the buffer capacity of mixtures of 0.1 N and 0.2 N acetic acid solutions with a strong acid or with alkali. We see that between pH s of 2 and 3.5 the total buffer capacity is obtained by adding the ordinates of the two dotted lines which represent the buffer capacities of the strong and weak acid. Outside this pH-region, we have to deal only with the buffer index of the individual weak acid, strong acid, or base, without having to consider their mutual buffering action. 

Most buffer solutions are composed of a weak acid and one of its alkali salts. Usually such mixtures of an acid and its salt may be prepared to extend over a range of two pH units, between pK 1 and pK — 1 where pK is the negative logarithm of the dissociation constant Ka) of the acid. Buffer solutions made with acetic acid, which has a dissociation constant of 1.86 X 10 or a pK of 4.73, are useful in the pH range between 3.7 and 5.7. It should be recalled that the intensity of buffer action (buffer capacity) in a series of 0.7 buffer solutions is greatest in the mixture of pH equal to pK, in which the ratio of acid to salt is unity (cf. Fig. 13). The greater the difference between pH and pK, the less pronounced becomes the buffer action. A solution in which the acid to salt ratio exceeds 10 be stored unchanged. 

The buffer range is the pH range over which the buffer acts effectively, and it is related to the relative component concentrations. The further the buffer-component concentration ratio is from 1, the less effective the buffering action (that is, the lower the buffer capacity). In practice, if the [A ]/[HA] ratio is greater than 10 or less than 0.1—that is, if one component concentration is more than 10 times the other—buffering action is poor. Recalling that log 10 = +1 and log... 

The original concept of pH-buffer action arose out of biochemical studies, and the need for pH control in all aspects of biological research is now universally recognized. Unfortunately, until recently there were few suitable substances having good buffering capacity in the physiologically... 

The equilibria represented by Eqs. (2.18) through (2.23) further indicate that as OH is introduced, then Eqs. (2.19) and (2.20) are displaced to the right, resulting in proton production. This opposes any rise in pH and accounts for the buffering capacity of seawater. Irrespective of this, however, Eqs. (2.18) through (2.23) indicate that this buffering action is accompanied by the formation of calcareous deposits on cathodic surfaces exposed to seawater. 

Most commercial carboxylated imidazoline surfactants are actually mixtures of classes 1 and 2 listed above, while the sulfated materials are combinations of classes 3 and class 4. The carboxylated materials will usually have a buffering action in solution so that the native pH will be slightly alkaline. The class 3 and class 4 materials possess slightly less buffering capacity, but will lie just to the acidic side. 

The most convincing proposal is that camosine plays one or more roles in control of intracellular hydrogen ion concentration (Abe, 2000 Vaughan-Jones et al, 2006). Camosine is an effective physiological buffer it is presumed that this property explains its predominant association with white, glycolytic, muscles which possess relatively few mitochondria and thereby generate lactic acid. Not only may camosine, also possible in its acetylated form, help to directly suppress the rise in hydrogen ion concentration but its ability to activate the enzyme carbonic anhydrase (Temperini et al, 2005) would increase bicarbonate buffer capacity. These properties may help explain camosine s protective action in ischaemia, a condition associated with severe intracellular acidosis. 

Probably an example and problems derived from the carbon dioxide-blood buffer system in humans should be in every physical chemistry course. What a rich, complex example this is from Henry s law for the solubility of carbon dioxide in water (blood) to buffer capacity, that is, the rate of change of the law of mass action with proton concentration. The example can be expanded to include nonideal solutions and activities. How many physical chemistry courses use this wonderful and terribly relevant to life example First-year medical students learn this material. 

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