Buffer action solutions

Adding as little as 0.1 mb of concentrated HCl to a liter of H2O shifts the pH from 7.0 to 3.0. The same addition of HCl to a liter solution that is 0.1 M in both a weak acid and its conjugate weak base, however, results in only a negligible change in pH. Such solutions are called buffers, and their buffering action is a consequence of the relationship between pH and the relative concentrations of the conjugate weak acid/weak base pair. 

Because of the zwitterion formation, mutual buffering action, and the presence of strongly acid components, soybean phosphoHpids have an overall pH of about 6.6 and react as slightly acidic in dispersions-in-water or in solutions-in-solvents. Further acidification brings soybean phosphoHpids to an overall isoelectric point of about pH 3.5. The alcohol-soluble fraction tends to favor oil-in-water emulsions and the alcohol-insoluble phosphoHpids tend to promote water-in-oil emulsions. 

The characteristics of soluble sihcates relevant to various uses include the pH behavior of solutions, the rate of water loss from films, and dried film strength. The pH values of sihcate solutions are a function of composition and concentration. These solutions are alkaline, being composed of a salt of a strong base and a weak acid. The solutions exhibit up to twice the buffering action of other alkaline chemicals, eg, phosphate. An approximately linear empirical relationship exists between the modulus of sodium sihcate and the maximum solution pH for ratios of 2.0 to 4.0. 

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. 

Because the ionic product of water = [H ] [OH ] = 1.04 x 10" at 25°C, it follows that pH = 14 - pOH. Thus, a neutral solution (e.g., pure water at 25°C) in which [H j = [OH ] has a pH = pOH = 7. Acids show a lower pH and bases a higher pH than this neutral value of 7. The hydrogen ion concentrations can cover a wide range, from -1 g-ion/liter or more in acidic solutions to -lO" " g-ion/liter or less in alkaline solutions [53, p. 545]. Buffer action refers to the property of a solution in resisting change of pH upon addition of an acid or a base. Buffer solutions usually consist of a mixture of a weak acid and its salt (conjugate base) or of a weak base and its salt (conjugate acid). 

These reactions have very large equilibrium constants, as we will see in Section 14.3, and so go virtually to completion. As a result, the added H+ or OH- ions are consumed and do not directly affect the pH. This is the principle of buffer action, which explains why a buffered solution is much more resistant to a change in pH than one that is unbuffered (Figure 14.1, p. 384). 

Before leaving the subject of buffer solutions, it is necessary to draw attention to a possible erroneous deduction from equation (21), namely that the hydrogen-ion concentration of a buffer solution is dependent only upon the ratio of the concentrations of acid and salt and upon Ka, and not upon the actual concentrations otherwise expressed, that the pH of such a buffer mixture should not change upon dilution with water. This is approximately although not strictly true. In deducing equation (18), concentrations have been substituted for activities, a step which is not entirely justifiable except in dilute solutions. The exact expression controlling buffer action is ... 

In some of the details which follow, reference is made to the addition of a buffer solution, and in all such cases, to ensure that the requisite buffering action is in fact achieved, it is necessary to make certain that the original solution has first been made almost neutral by the cautious addition of sodium hydroxide or ammonium hydroxide, or of dilute acid, before adding the buffer solution. When an acid solution containing a metallic ion is neutralised by the addition of alkali care must be taken to ensure that the metal hydroxide is not precipitated. 

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... 

We can use these numbers to express the range of buffer action in terms of the pH of the solution. The Henderson-Hasselbalch equation shows us that,... 

Biochemists and molecular biologists use phosphate buffers to match physiological conditions. A buffer solution that contains H2 PO4 as the weak acid and HP04 as the weak base has a pH value very close to 7.0. A biochemist prepares 0.250 L of a buffer solution that contains 0.225 M HP04 and 0.330 M H2 PO4. What is the pH of this buffer solution Is the buffering action of this solution destroyed by addition of 0.40 g NaOH ... 

Use the seven-step strategy to calculate the pH of the buffer solution using the buffer equation. Then compare the amount of acid in the solution with the amount of added base. Buffer action is destroyed if the amount of added base is sufficient to react with all the acid.The buffering action of this solution is created by the weak acid H2 PO4 and its conjugate base HP04. The equilibrium constant for this... 

Point A iies aiong the section of the titration curve known as the buffer region. Buffering action comes from the presence of a weak acid and its conjugate base as major species in solution. Moreover, Point A iies beyond the midpoint of the titration, which teiis us that more than half of the weak acid has been consumed. We represent this soiution with two moiecuies of H four ions of A, and four H2 O moiecuies ... 

Because trls has only meager buffering action at pH 6.1, fluctuations In the pH of Ion exchanger and solutions may occur and may result In abnormal chromatographic behavior. Buffered conditions may be obtained by substituting bls-trls which has a pK of about 6.5, and virtually Identical behavior results If Developer A Is constituted with 0.03 M bls-trls-HCl 0.03 M NaCl 0.01% KCN at pH 6.2. 

Solutions which resist changes in their pH values on the addition of small amounts of acids or bases are called buffer solutions or simply buffers. The resistance to a change in the H+ ion concentration on the addition of an acid or an alkali is known as buffer action. Just as the buffer of railway carriages resists shocks, similarly buffer solutions resist the action of various substances which can affect the pH value. There are two types of buffers (i) acidic buffer and (ii) basic buffer. 

Buffers are compounds or mixtures of compounds that, when present in solution, resist changes in pH upon the addition of small amounts of acids or alkali. In essence, they are capable of maintaining the pH values relatively constant and, therefore, are insensitive towards addition of small quantities of acids and/or bases. The ability to resist changes in pH is called buffer action. Buffers are added to topical formulations to control the pH that provides an acceptable balance between chemical stability, therapeutic activity, and comfort. 

Buffers contain mixtures of weak acids and their salts (i.e., the conjugate bases of acids), or mixtures of weak bases and their conjugate acids. Typical buffer systems used in pharmaceutical dosage forms include mixtures of boric acid and sodium borate, acetic acid and sodium acetate, and sodium acid phosphate and disodium phosphate. The reason for the buffering action of a weak acid, HA (e.g., acetic acid) and its ionized salt, A" (e.g., sodium acetate) is that A" ions from the salt combine with the added hydrogen ions, removing them from solution as undissociated weak acid. 

The CMC of C14DAO is about 1 x 10 M at 25 C. Below the CMC a typical buffering action is observed (4 x ICT M), above the CMC the titration curves are slanted toward lower pH s with increasing HCl concentration 0.2 M having a steeper slope than 8 X 10 M. Addition of SDS to a solution of C DAO affects the HCl titration curve markedly and will be discussed later. 

Solutions in which the buffering action is due to the solvent rather than any added solute Strongly acidic or basic aqueous solutions will show httle change in pH when additional increments of acid or base are added (recall that the pK value for H3O+ is -1.74, and that for H2O is 15.74) . Because the solvent is in such high concentration, the buffering capacity for pseudo buffers is larger than for conventional buffers. See Buffer Capacity... 

Takakura, K. Ishikawa, M. Ito, T. Action spectrum for the induction of single-strand breaks in DNA in buffered aqueous solution in the wavelength range from 150 to 272 nm dual mechanism. Int. J. Radiat. Biol. 1987, 52 (5), 667-675. 

As well as this buffering action, addition of ammonium ion also decreases the pH of an ammonia solution as shown above. This is an important effect—more important than the buffering action in many CD processes. 

Carbonic acid, H2CO3, is a weak acid that dissociates by the above reaction (B). In general, a solution of a weak acid HA that dissociates into H and A will serves as a buffer solution. Thus, respiration in lungs contributes to physiological buffer actions. 

The above conceptual and operational pH definitions for solutions in non-aqueous and mixed solvents are very similar to those for aqueous solutions [16]. At present, pH values are available for the RVS and some primary standards in the mixtures between water and eight organic solvents (see 5 in Section 6.2) [17]. If a reliable pH standard is available for the solvent under study, the pH can be determined with a pH meter and a glass electrode, just as in aqueous solutions. However, in order to apply the IUPAC method to the solutions in neat organic solvents or water-poor mixed solvents, there are still some problems to be solved. One of them is that it is difficult to get the RVS in such solvents, because (i) the solubility of KHPh is not enough and (ii) the buffer action of KHPh is too low in solutions of an aprotic nature [18].8) Another problem is that the response of the glass electrode is often very slow in non-aqueous solvents,9 although this has been considerably improved by the use of pH-ISFETs [19]. Practical pH measurements in non-aqueous solutions and their applications are discussed in Chapter 6. 

The problem with the tetraalkylammonium hydrogen phthalate or maleate solution in y-BL is that the solution has no pH-buffer action (Section 6.2.2). On rare occasions, the solution near the cathode of the capacitor locally... 

Experiments with house flies pointed to a considerable buffering action in the intestine.3 Solutions of arsenious acid and of the stoichiometric quantities of sodium hydroxide and arsenious oxide to form normal sodium arsenite, containing 15 g. of sucrose per 100 c.c., were fed to adult flies. The pH values of the former solutions were 6-58 to 6-96 and of the latter 11-3 to 11-4, but the toxicities were equal, being 0-14 mg. As per g. body weight—a large value for an insect. None of these solutions was repellent to the flies, but if the pH was increased beyond 11-4 repellent action was observed house fly bait therefore should not contain more alkali than is necessary to hold the arsenic in solution. The eradication of the tsetse fly by similar means is difficult. There is not much chance of a poisonous dose being taken from the skin of a dipped animal, but a toxic dose can be taken up from an arsenic-impregnated area by means of the proboscis.4... 

Mixed Solutions and Buffers 11.1 Mixed Solutions 1 1.2 Buffer Action 11.3 Designing a Buffer 1 1.4 Buffer Capacity... 

Just as a sponge can hold only so much water, a buffer can also run out of mopping-up power. Its proton sources and sinks become exhausted if too much strong acid or base is added to the solution. Buffer capacity is the amount of acid or base that can be added before the buffer loses its ability to resist the change in pH. A buffer with a high capacity can maintain its buffering action longer than can one with only a small capacity. 

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