The buffering capacity

During the determination of the buffering capacity, two series of weighed amounts of the soil are used HCl and NaOH are stepwise added to the first 

Carbonates in soil occur mainly in the form of CaCOg with a smaller portion ofMgC03. The remaining forms are determined only in special cases. Their determination is based on their easy decomposition with diluted acids  

The amount of CO2 released serves as a measure for determining the carbonate content on the basis of visible estimation, or of a gravimetric or volumetric method. 

The visual estimation is performed under field conditions by dropping 10% HCl onto a soil clod and observing its decomposition. Depending on the intensity of the gas release the CaCOg is estimated as follows hardly observable, short-term effervescence 0.3% CaCOg weak, short-term effervescence distinct effervescence violent effervescence with long-term decomposition 

The gravimetric method is, however, the most precise. It is based on measuring the decrease of the sample weight after decomposing carbonates with acids with simultaneous heating of the sample. 

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Between various wood species great differences can occur in pH as well as in the buffer capacity. Even within the same wood species, differences might occur due to seasonal variations, portion of the wood substance under investigation, pH of the soil, age of the tree, time span after cutting, drying and processing parameters. 

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. 

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. 

The buffer capacity indicates how much OH or H+ ions a buffer can react with. What is the buffer capacity of the buffers in Problem 9 ... 

In general, we may state that the buffering capacity is maintained for mixtures within the range 1 acid 10 salt and 10 acid l salt and the approximate pH range of a weak acid buffer is ... 

The concentration of the acid is usually of the order 0.05-0.2 mol L" Similar remarks apply to weak bases. It is clear that the greater the concentrations of acid and conjugate base in a buffer solution, the greater will be the buffer capacity. A quantitative measure of buffer capacity is given by the number of moles of strong base required to change the pH of 1 litre of the solution by 1 pH unit. 

R FS. 0.05m Potassium hydrogenphthalate. Dissolve 10.21 g of the solid (dried below 130 °C) in water and dilute to 1 kg. The pH is not affected by atmospheric carbon dioxide the buffer capacity is rather low. The solution should be replaced after 5-6 weeks, or earlier if mould-growth is apparent. 

Fruit and vegetable juices packed with 21-26 in. of vacuum and stored in uncoated aluminum cans caused severe corrosion as shown in Table III. The corrosion rate brought about by the juices depends more on the nature of the organic acid present and the buffering capacity of the juice than on the total titratable acidity (11). The use of coated aluminum containers considerably minimized corrosion problems. Product control under extended storage conditions may be achieved by using specific chemical additives. However, more work is needed in this area before final conclusions can be reached. 

The susceptibility of the sulfamates to hydrolysis is intermediate with respect to procedures commonly used for extraction and manipulation of extracts. Quantitative hydrolysis of the pure sulfamate toxins can be accomplished (9) by heating at 100 C for 5 min in the presence of not less than 0.1 M free acid (pH 1 or below). Milder conditions appear insufficient (10). Figure 9 summarizes results from two separate experiments in which samples of nontoxic clam flesh, enriched with constant amounts of saxitoxin Cl (4), were acidified to differing final concentrations of HCl and heated for 5 min at 100 C. The difference between 0.1 M HCl, which would be sufficient for hydrolysis of the pure toxin, and the HCl concentration required to attain plateau toxicity, probably reflects the buffer capacity of... 

When small amounts of hydronium or hydroxide ions are added to a buffer solution, the pH changes are very small. There is a limit, however, to the amount of protection that a buffer solution can provide. After either buffering agent is consumed, the solution loses its ability to maintain near-constant pH. The buffer capacity of a solution is the amount of added H3 O or OH that the buffer solution can tolerate without exceeding a specified pH range. 

CI8-OOI2. A student adds 30. mL of 5.00 M HCl to the buffer solution described in Section Exercise 18.1.3. Is the buffering capacity of the solution destroyed What is the final pH of the solution ... 

Twenty-three kinetics have been carried out at 25°C for pH values from 8.25 to 11.25. The rate constant, calculated as the average of all the ks, was of 27.2 9.0 mol 1 min. The pH correction according to equation (2) was not perfect, as there was a tendency to obtain higher k values at lower pH values. However, this was specially true for extreme vdues of our pH range, where the buffer capacity of ethanolamine was limited (higher pHs) or the reaction proceeded very slowly (low pHs), impairing the precision of the data. Another factor that might explain the dispersion of the data is lack of precision of pH measurement (no better than 0.02 pH units). 

During the lifetime of a root, considerable depletion of the available mineral nutrients (MN) in the rhizosphere is to be expected. This, in turn, will affect the equilibrium between available and unavailable forms of MN. For example, dissolution of insoluble calcium or iron phosphates may occur, clay-fixed ammonium or potassium may be released, and nonlabile forms of P associated with clay and sesquioxide surfaces may enter soil solution (10). Any or all of these conversions to available forms will act to buffer the soil solution concentrations and reduce the intensity of the depletion curves around the root. However, because they occur relatively slowly (e.g., over hours, days, or weeks), they cannot be accounted for in the buffer capacity term and have to be included as separate source (dCldl) terms in Eq. (8). Such source terms are likely to be highly soil specific and difficult to measure (11). Many rhizosphere modelers have chosen to ignore them altogether, either by dealing with soils in which they are of limited importance or by growing plants for relatively short periods of time, where their contribution is small. Where such terms have been included, it is common to find first-order kinetic equations being used to describe the rate of interconversion (12). 

FIG. 14 A model for the uptake of weakly basic compounds into lipid bilayer membrane (inside acidic) in response to the pH difference. For compounds with appropriate pki values, a neutral outside pH results in a mixture of both the protonated form AH (membrane impermeable) and unprotonated form A (membrane permeable) of the compound. The unprotonated form diffuse across the membrane until the inside and outside concentrations are equal. Inside the membrane an acidic interior results in protonation of the neutral unprotonated form, thereby driving continued uptake of the compound. Depending on the quantity of the outside weak base and the buffering capacity of the inside compartment, essentially complete uptake can usually be accomplished. The ratio between inside and outside concentrations of the weakly basic compound at equilibrum should equal the residual pH gradient. 

Protonated THAM (with CP or HCO, ) is excreted in the urine at a rate that is slightly higher than creatinine clearance. As such, THAM augments the buffering capacity of the blood without generating excess C02. THAM is less effective in patients with renal failure and toxicities may include hyperkalemia, hypoglycemia, and possible respiratory depression. 

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... 

Parenteral products should be formulated to possess sufficient buffer capacity to maintain proper product pH. Factors that influence pH include product degradation, container and stopper effects, diffusion of gases through the closure, and the effect of gases in the product or in the headspace. However, the buffer capacity of a formulation must be readily overcome by the biological fluids thus, the concentration and ratios of buffer ingredients must be carefully selected. 

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,... 

Thus, the buffering capacity depends on the composition of the buffer, i.e. on the concentration of the salt a or b. The maximum value found by differentiation of Eq. (1.4.27) with respect to a corresponds, for an acidic buffer, to b = s. 

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. 

When calcium carbonate goes into solution, it releases basic carbonate ions (COf ), which react with hydrogen ions to form carbon dioxide (which will normally remain in solution at deep-well-injection pressures) and water. Removal of hydrogen ions raises the pH of the solution. However, aqueous carbon dioxide serves to buffer the solution (i.e., re-forms carbonic acid in reaction with water to add H+ ions to solution). Consequently, the buffering capacity of the solution must be exceeded before complete neutralization will take place. Nitric acid can react with certain alcohols and ketones under increased pressure to increase the pH of the solution, and this reaction was proposed by Goolsby41 to explain the lower-than-expected level of calcium ions in backflowed waste at the Monsanto waste injection facility in Florida. 

At equilibrium, the concentration of H+ will remain constant. When a strong acid (represented by H+ or HA) is introduced into solution, the concentration of H+ is increased. The buffer compensates by reacting with the excess H ions, moving the direction of the above reaction to the left. By combining with bicarbonate and carbonate ions to form the nonionic carbonic acid, equilibrium is reestablished at a pH nearly the same as that existing before. The buffer capacity in this case is determined by the total concentration of carbonate and bicarbonate ions. When no more carbonate or bicarbonate ions are available to combine with excess H+ ions, the buffer capacity has been exceeded and pH will change dramatically upon addition of further acid. 

If the buffering capacity of the electrolyte is significant and the association/dissociation rates are very fast so that the corresponding two terms dominate all the others, then... 

One can see no way in which the halides could affect the buffering capacity of these electrolytes. There, indeed, seems to be little doubt that adsorption of the halides at the oxide surface takes place and plays a significant role. 

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... 

Respective weathering rates of sulfide minerals is pyrrhotite/sphalerite>pyrite. The buffering capacity of the tailings is low due to the lack of carbonates, allowing the rapid onset of low pH conditions. 

Buffers are used mainly to control the pH and the acid-base equilibrium of the solute in the mobile phase. They can also be used to influence the retention times of ionizable compounds. The buffer capacity should be maximum and should be uniform in the pH range of 2-8 commonly used in HPLC. The buffers should be soluble, stable, and compatible with the detector employed, e.g., citrates are known to react with certain HPLC hardware components. 

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