Buffer intensity

We can consider this equilibrium in isolation from the two other equilibria if the pif values differ by more than about 2 pH units. This condition is met for phosphoric acid where pff a.i =2,1, pffa.2 =7,2, and P a.3=12.3. For plTa.2 =7.2, Eq. 4-79 becomes 

Again [H2PO4 ] and [HP04 ] are much greater than [H ] and [OH ) at this pH so our assumption of complete reaction is valid. The reader may wish to prove this using the approach given in Example 4-27. 

Buffer intensity, j3, or buffer capacity, as it is often called, is defined as the moles/liter of strong base, Cb, (or OH ) which when added to a solution causes a unit change in pH. Thus 

C = ((sample volume, liters)/(normality of titrant))(10 ml/liter) 

Therefore, the reciprocal of the slope of the titration curve is proportional to the buffer intensity. For example, the titration curve for 10 M HAc (Fig. 4-12) is reproduced in Fig. 4-14 together with a plot of derived from slope measurements on this curve. 

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Sa.tura.tion Index. Materials of constmction used in pools are subject to the corrosive effects of water, eg, iron and copper equipment can corrode whereas concrete and plaster can undergo dissolution, ie, etching. The corrosion rate of metallic surfaces has been shown to be a function of the concentrations of Cl ,, dissolved O2, alkalinity, and Ca hardness as well as buffer intensity, time, and the calcium carbonate saturation index (35). 

The buffer capacity of the pit fluid is equal to the change in alkalinity of the system per unit change of pH. Figure 4-491 shows the buffer intensity (capacity) of a 0.1 M carbonate pit fluid. Calculating the initial buffer capacity of the pit fluid allows for prediction of the pH change upon introduction of live acid and also any addition of buffer, such as sodium bicarbonate, required to neutralize the excess hydrogen ions. 

Molecular diffusion coefficient of the solute in the buffer Intensity of electric field... 

Whittier, E. 0. 1933A. Buffer intensities of milk and milk constituents. III. Buffer action of calcium phosphate. J. Biol. Chem. 102, 733-747. 

The view has long been held that hydrogen-ion buffeting in the oceans is due to the CO2—HCO3-— CC>3 equilibrium. Within recent years this view has been challenged, and the importance of aluminosilicate equilibria in maintaining the pH of sea water emphasized. The buffer intensity of a system is of thermodynamic nature and is defined as... 

Fig. 3. Buffer intensity as a function of pH for some homogeneous and heterogeneous chemical systems. The buffer intensities ate defined for. llvit,.,...

CO2—HCOj —COr". However, large incremental additions of acid or base or additrons over a duration of time would involve the heterogeneous carbonate and aluminosilicate equilibria the relative importance of each would depend on the buffer intensities of the various equilibria and the relative rates of aluminosilicate and carbonate reactions. 

Figure 19.6 illustrates how we process the two-energy data and generate the ASAXS profiles. First, we average the set of all DNA and buffer intensity profiles at each of the two energies. The averaged data are displayed in Fig. 19.6A. Note that both DNA and buffer profiles, taken at Eon, have slighdy elevated background relative to Eofr data this is due to X-ray fluorescence. Most of this fluorescence background is removed by buffer subtraction (see Fig. 19.6B). The remaining on-edge fluorescence results...

Hydrogen ion regulation in natural waters is provided by numerous homogeneous and heterogeneous buffer systems. It is important to distinguish in these systems between intensity factors (pH) and capacity factors (e.g., the total acid- or base-neutralizing capacity). The buffer intensity is found to be an implicit function of both these factors. In this chapter, we discuss acid-base equilibria primarily from a general and didactic point of view. In Chapter 4 we address ourselves more specifically to the dissolved carbonate system. 

Figure 3.10. Equilibrium composition, buffer intensity, and titration curve of diprotic acid-base system, (a) Species distribution, (b) Buffer intensity, (c) Titration curve. The equivalence points, x, y, and z (a), are representative of the composition of pure solutions of H2L NaHL, and Na2L respectively, and correspond to minima in the buffer intensity. The smaller the buffer intensity, the steeper is the titration curve.

The slope of a titration curve (pH versus Cb) is related to the tendency of die solution at any point in the titration curve to change pH upon addition of base. The buffer intensity at any point of the titration is inversely proportional to the slope of the titration curve at that point and may be defined as... 

Obviously the buffer intensity can be expressed numerically by differentiating the equation defining the titration curve with respect to pH. For a monoprotic acid-base system (see equations 67 and 69). 

Aqueous solutions are well buffered at either extreme of the pH scale. If in an alkalimetric or acidimetric titration curve the pH at the equivalence point falls into a pH range where the buffer intensity caused by [H ] or [OH ] exceeds that of the other protolytes, obliteration of a pH jump at the equivalence point results (see Figure 3.11). The concept of pH buffers can be extended to ions other than H" ". Metal-ion buffers will be discussed in Chapter 6. 

If various acid-base pairs—HA, A HB, B and so on—are present in the solution, the buffer intensity is given by... 

Polyprotic Systems In the same fashion as equation 91 has been derived, expressions for the buffer intensity of polyprotic acid-base systems can be developed. In Table 3.8, the buffer intensity of a diprotic acid-base system is derived. A polyprotic acid can be treated the same way as a mixture of indi-... 

Figure 3.11. Alkalimetric titration of a weak acid (10 M boric acid), (a) Equilibrium distribution, (b) Buffer intensity, (c) Alkalimetric titration. No pH jump occurs at the equivalence point (/ = 1) because of buffering by OH ions.

The concept of buffer intensity considered above may be extended and defined in a generalized way for the incremental addition of a constituent to a closed system at equilibrium. Thus, in addition to the buffer intensity with respect to strong acids or bases, buffer intensities with respect to weak acids... 

Buffer Intensity and Neutralizing Capacity 137 Table 3.8. Titration Curve and Buffer Intensity of a Two-Protic Acid (H2C)"... 

Arrange the following solution in order of increasing buffer intensity ... 

Obviously the diagrams for fresh water and for seawater are generally similar but differ in certain details, for example, the buffer intensity at high pH, point z. Because of the ionic strength effects, the operational acidity constants are larger for seawater than for fresh waters that is, the p/T values and thus the pH at the equivalence point—especially at the equivalence point y— are lower for seawater than for fresh water. Seawater contains, in addition to dissolved CO2, boric acid, H3BO3 (representative concentration of total boi on = 4.1 X 10 M). Its presence does not contribute markedly to the buffering of seawater. At the pH of seawater (pH = 8.1), its buffer intensity is near the minimum. 

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