Buffered systems buffering capacity

Flue Ga.s Desulfuriza.tion. Citric acid can be used to buffer systems that can scmb sulfur dioxide from flue gas produced by large coal and gas-fired boilers generating steam for electrical power (134—143). The optimum pH for sulfur dioxide absorption is pH 4.5, which is where citrate has buffer capacity. Sulfur dioxide is the primary contributor to acid rain, which can cause environmental damage. 

When a forest system is subjected to acid deposition, the foliar canopy can initially provide some neutralizing capacity. If the quantity of acid components is too high, this limited neutralizing capacity is overcome. As the acid components reach the forest floor, the soil composition determines their impact. The soil composition may have sufficient buffering capacity to neutralize the acid components. However, alteration of soil pH can result in mobilization or leaching of important minerals in the soil. In some instances, trace metals such as Ca or Mg may be removed from the soil, altering the A1 tolerance for trees. 

A second way to achieve constancy of a reactant is to make use of a buffer system. If the reaction medium is water and B is either the hydronium ion or the hydroxide ion, use of a pH buffer can hold Cb reasonably constant, provided the buffer capacity is high enough to cope with acids or bases generated in the reaction. The constancy of the pH required depends upon the sensitivity of the analytical method, the extent of reaction followed, and the accuracy desired in the rate constant determination. 

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. 

The pH then remains relatively constant. The components of a buffer system are chosen such that the of the weak acid is close to the pH of interest. It is at the that the buffer system shows its greatest buffering capacity. At pH values more than one pH unit from the buffer systems become ineffec-... 

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. 

With a given weak acid, a buffer soiution can be prepared at any pH within about one unit of its p vaiue. Suppose, for exampie, that a biochemist needs a buffer system to maintain the pH of a soiution ciose to 5.0. What reagents shouid be used According to the previous anaiysis, the weak acid can have a p Z a between 4.0 and 6.0. As the p deviates from the desired pH, however, the soiution has a reduced buffer capacity. Thus, a buffer has maximum capacity when its acid has its p as ciose as possibie to the target pH. Tabie 18-1 iists some acid-base pairs often used as buffer soiutions. For a pH - 5.0 buffer, acetic acid (p Za — 4.75) and its conjugate base, acetate, wouid be a good choice. 

The ICl-CaC03 procedure required a filtration to remove insoluble, inorganic by-products prior to biphasic extraction. In an effort to develop a homogeneous process for the iodination step, a pH control protocol was later implemented in the manufacturing process. The pH-controlled iodination was run in a single phase in a MeOH-water system by simultaneous addition of the aqueous IC1 solution and 1M NaOH. Citric acid was added to increase the buffer capacity to the optimal pH (5-5.5) for robust operation. Under these conditions, the iodoaniline 28 was typically obtained in >99 A% with <1% of diiodoaniline 32. Residual... 

Another formulation variable that must be considered is that of the solution pH and bulfer capacity. Since the anterior chamber fluid (aqueous humor) contains essentially the same buffering systems as the blood, products with a pH outside the physiological range of 7.0-7.4 are converted to this range by the buffering capacity of the aqueous humor if a relatively small volume of the solution is introduced. Often,... 

The slope of the tangent to the curve at the inflection point where oc = is thus inversely proportional to the number of electrons n. The E-oc curves are similar to the titration curves of weak acids or bases (pH-or). For neutralization curves, the slope dpH/doc characterizes the buffering capacity of the solution for redox potential curves, the differential dE/da characterizes the redox capacity of the system. If oc — for a buffer, then changes in pH produced by changes in a are the smallest possible. If a = in a redox system, then the potential changes produced by changes in oc are also minimal (the system is well poised ). 

Ecologically, accidental releases of solution forms of hydrochloric acid may adversely affect aquatic life by including a transient lowering of the pH (i.e., increasing the acidity) of surface waters. Releases of hydrochloric acid to surface waters and soils will be neutralized to an extent due to the buffering capacities of both systems. The extent of these reactions will depend on the characteristics of the specific environment. 

A mixture of sodium hydroxide and sodium carbonate, a metering pump being necessary. This method avoids the use of either silicate or phosphate and is popular for woven goods and in circumstances where silicate would pose problems. Ideally the carbonate should be free from bicarbonate. This system has less buffering capacity and gives slightly lower bath stability than methods (1) and (2). 

Rosing, M. T., 1993, The buffering capacity of open heterogeneous systems. Geochimica et Cosmochimica Acta 57, 2223-2226. 

Recent studies demonstrated that the composition of the reaction mixture, and in particular the pH have significant effects on the kinetics of iron(III)-catalyzed autoxidation of sulfur(IV) oxides. When the reaction was triggered at pH 6.1, the typical pH profile as a function of time exhibited a distinct induction period after which the pH sharply decreased (98).The S-shaped kinetic traces were interpreted by assuming that the buffer capacity of the HSO3 / SO3- system efficiently reduces the acidifying effect of the oxidation process. The activity of the... 

It is the chemical buffering system which contributes significantly to the carrying capacity of a soil [ 17]. In general, any soil cannot completely adsorb all the pollutants from the liquid solution. There is an equilibrium between solvent and solution phases. The amount left in solution gradually increases as the buffer capacity of the soil is approached. 

The two lower pH levels were phosphate buffers whereas the 8.6 buffer consisted of a boric acid, sodium borate system. The buffers showed no reaction with pretreatment chemicals used, and had sufficient buffer capacity to maintain constant pH during experiments of long duration. 

The pH value is kept constant by buffer systems that cushion minor disturbances in the acid-base balance (C). In the longer term, the decisive aspect is maintaining a balanced equilibrium between H" production and uptake and H" release. If the blood s buffering capacity is not suf cient, or if the acid-base balance is not in equilibrium—e.g., in kidney disease or during hypoventilation or hyperventilation-shifts in the plasma pH value can occur. A reduction by more than 0.03 units is known as acidosis, and an increase is called alkalosis. 

The buffering capacity of a buffer system depends on its concentration and its pKg value. The strongest effect is achieved if the pH value corresponds to the buffer system s pKa value (see p. 30). For this reason, weak acids with pKa values of around 7 are best suited for buffering purposes in the blood. 

The second dissociation step in phosphate (H2P04/HP04 ) also contributes to the buffering capacity of the blood plasma. Although the pKa value of this system is nearly optimal, its contribution remains small due to the low total concentration of phosphate in the blood (around 1 mM). 

Kuo, R.J. Matijevic, E. (1980) Particle adhesion and removal in model systems. III. Monodisperse ferric oxide on steel. J. Colloid Interface Sci. 78 407-421 Kuo, S. Jellum, E.J. (1994) The effect of soil phosphorus buffering capacity on phosphorus extraction by iron oxide-coated paper strips in some acid soils. Soil Sci. 158 124-131... 

You carry out a reaction in an organic solvent. The reaction is catalysed by a lipase immobilised by adsorption on a porous support. The reaction virtually stops long before equilibrium is reached and you suspect that this can be due to the formation of an acidic reaction product. What can you do to increase the buffering capacity of the system ... 

---