Acetate, buffer capacity

Utilize the general form of the acetic acid-acetate buffer capacity curve obtained in Problem 11 to draw an approximate curve for the buffer capacity over the range of pH from 2 to 13 of the universal buffer mixture described on page 415. It may be assumed that the total concentration of each acid and its salt is always 0.2 molar. 

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... 

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. 

To test the robustness of the formulation to variations in gastric pH, dissolution results should be obtained in both the pH 2 medium described in Table 3 and a model which reflects the conditions in the hypochlohydric stomach. A good choice would be acetate buffer adjusted to pH 5 and having a very low buffer capacity, since hypochlorhydria is generated by a reduction in HCl secretion rather than the addition of buffer species. 

Buffer solutions have two important characteristics. One of these characteristics is the pH of the solution. The other is its buffer capacity the amount of acid or base that can be added before considerable change occurs to the pH. The buffer capacity depends on the concentration of the acid/conjugate base (or the base/conjugate acid) in the buffer solution. When the ratio of the concentration of the buffer components is close to 1, the buffer capacity has reached its maximum. As well, a buffer that is more concentrated resists changes to pH more than than a buffer that is more dilute. This idea is illustrated in Figure 8.10, with buffer solutions of acetic acid and acetate of different concentrations. 

The LDso values for picric acid after oral dosing of male and female rats were 290 and 200 mg/kg, respectively. Death was due to severe acidosis, with toxic doses of picric acid exceeding the buffering capacity of the blood. In rats, metabolism of picric acid is primarily limited to reduction of nitro groups of the aromatic ring and subsequent conjugation by acetate. 

Lobacz et al. [52] have described partial adsorption ofTl+-cryptand (2,2,2) complex on mercury electrode. From voltocoulom-etry, cyclic voltammetry, and chrono-coulometry, it has been deduced that electroreduction of this complex proceeds via two parallel pathways from the solution and from the adsorbed states, which are energetically close. Also, Damaskin and coworkers [53] have studied adsorption of the complexes of alkali metal cations with cryptand (2,2,2) using differential capacity measurements and a stationary drop electrode. It has been found that these complexes exhibit strong adsorption properties. Novotny etal. [54] have studied interfacial activity and adsorptive accumulation of U02 " "-cupferron and UO2 - chloranilic acid complexes on mercury electrodes at various potentials in 0.1 M acetate buffer of pH 4.6 and 0.1 M NaCl04, respectively. 

To appreciate the ability of a buffer solution to maintain a nearly constant pH, let s contrast the behavior of the 0.10 M acetic acid-0.10 M sodium acetate buffer with that of a 1.8 X 10 5 M HC1 solution. This very dilute HC1 solution has the same pH (4.74) as the buffer solution, but it doesn t have the capacity to soak up added... 

FIGURE 2.7 Buffer capacity of acetate buffer with respect to pH ( C = 0.05M ). 

The variation of buffer capacity of the acetate buffer with respect to pH is shown in Figure 2.7 for the total concentration of 0.05 M. 

M NaOH was added to a buffer containing 0.1 M sodium acetate and 0.1 M acetic acid. What is the buffer capacity of the solution ... 

The production rate is ultimately determined by the conditions in the reactor. Thus, after a change in the product flow- from the decanter there is a temporary difference between what is produced in the reactor and what is removed from the plant. This imbalance disappears after the reactor conditions are adjusted. For this scheme to work there must be enough internal buffer capacity to accommodate the reactor s temporary over-production or under-production of vinyl acetate. 

Plot the pH-buffer capacity curve for mixtures of acetic acid and sodium acetate of total concentration 0.2 n. Points should be obtained for mixtures containing 10, 20, 30, 40, 50, 60, 70, 80 and 90 per cent of sodium acetate, the pH s being estimated by the approximate form of the Henderson equation. Plot the buffer capacity curve for water at pH s 1, 2, 3 and 4, and superimpose the result on the curve for acetic acid. 

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