Buffer power

In the simplest case, a linear relationship may exist between solutes in soil solution and those on the solid pha.se, such that C, = hCr, where C, is the. solute concentration on the solid phase and h defines the buffer power. In perhaps more typical situations, the relationship might be defined by a more complicated, concentration-dependent relationship such as a Freundlich or Langmuir expression here the instantaneous buffer power may be defined as the tangent to the exchange isotherm i.e., h = dCJdCi. Some care is needed when defining this buffer power (7). 

Such an analysis indicates that the zero-sink assumption must be used with extreme caution if accurate flux calculations are required at the local root level. Potassium, for example, is close to the limiting value of A, for the zero sink assumption to be fulfilled, and simulations with larger roots or larger buffer powers could well lead to inaccurate simulation results. Any zero-sink model involving nitrate should be treated with some suspicion. The zero-sink assumption is also widely used in root architecture models (see later). 

This derivative is the reciprocal of the buffer power and describes the distribution of the diffnsing solute between the soil solid and solntion. Its value varies by... 

The term 9[HB]/9x in Equation (2.27) is expressed in terms of 9[HS]/9x as follows. The pH buffer power of each acid-base pair is defined as ... 

It is often found empirically that the change in soil pH for a given addition of acid or base is constant over a wide range of pH and this relation is not greatly altered by soil reduction. Hence the pH buffer power, 7>hs, is constant and... 

Figure 4.7 Calculated changes in pe, pH, [O2] and [Fe +] in an idealized soil during reduction. Mineral phases Fe(OH)3 and Fe3(OH)g. Parameters for pH buffering and cation exchange differ between (a)-(d) as indicated. Units of fees (soil pH buffer power), mmolkg pH CEC (initial cation exchange capacity), cmolc kg and [X ]l (concentration of non-carbonate anions), mM. CO2 pressure = lOkPa, 9 = 0.6, p = 1.0, initial pH = 4.5...

Figure 4.18 Sensitivity of the model used for the calculations in Figure 4.17 to its parameters [Fe] is the initial concentration of mobile Fe +, i>Fe is the soil Fe buffer power, i>HS is the soil pH buffer power, is the Fe + oxidation rate constant and p is the soil bulk density. Standard values as for calculations in Figure 4.17...

Fe(II) oxidation was comparable to that released from the roots to balance excess cation uptake. But in both soils the H+ generated in these two processes exceeded the acidification calculated from the pH profile and the soil pH buffer powers. This was possibly because of CO2 uptake by the roots and, in the Maahas soil, where acidity diffusion was fast because of the high pH and high CO2 pressure, because the acidification spread beyond the zone of soil analysed. 

FIGURE 2-17 The titration curve of acetic acid. After addition of each increment of NaOH to the acetic acid solution, the pH of the mixture is measured. This value is plotted against the amount of NaOH expressed as a fraction of the total NaOH required to convert all the acetic acid to its deprotonated form, acetate. The points so obtained yield the titration curve. Shown in the boxes are the predominant ionic forms at the points designated. At the midpoint of the titration, the concentrations of the proton donor and proton acceptor are equal, and the pH is numerically equal to the pAfa. The shaded zone is the useful region of buffering power, generally between 10% and 90% titration of the weak acid. 

Finally, as pointed out earlier, under the general condition of free and open exposure to the aqueous environment, only histidine has an R group (pKa = 6.0) providing significant buffering power near the neutral pH usually found in the intracellular and extracellular fluids of most animals and bacteria (Table 3-1). 

The rare-earth metals may have some buffering power. 

The equilibria involving protons and the substances which bind them are among the most important in dairy chemistry. The ionized and ioni-zable components of milk are in a state of rather delicate physical balance. Certain treatments which alter the state of dispersion of proteins and salts are reflected in the status of the protons. Thus the intensity (pH) and capacity (buffer power) factors of the acid-base equilibria have come to be widely used in processing control. 

The buffering power of arsenic acid towards alkali is considerable, and much greater than that of phosphate or citrate buffers.13... 

However, La Lande has shown that properly calcined bauxite develops color removal, ash removal, and alkaline buffering powers comparable to those of bone char.11 Bauxite and hydroxyapatite therefore appear... 

These three atoms can accept electrons but not give up electrons without change in valence. 6 The rare-earth metals may have some buffering power. 

From the analysis of the figures relative to the extraction processes, it can be noted that the dissolution kinetics are generally fast. The exception to this rule is the dissolution of Zn(II) and Fe(II) with EDTA for which the kinetics trend is very slow and the equilibrium conditions are not established after 24 hours. The trend of pH versus extraction time for EDTA solutions shown in Fig. 1 shows that the sludge has a characteristic buffer power, strongly conditioned... 

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