Buffers action

A pH of 6-0-6-5 is generally ensured by the buffering action of the ammonia produced by hydrolysis upon the hexamine salt.)... 

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. 

Addition of acetic or mineral acid to skimmed milk to reduce the pH value to 4.6, the isoelectric point, will cause the casein to precipitate. As calcium salts have a buffer action on the pH, somewhat more than the theoretical amount of acid must be used. Lactic acid produced in the process of milk souring by fermentation of the lactoses present by the bacterium Streptococcus lactis will lead to a similar precipitation. 

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. 

Pufferung,/. buffering cushioning. Puffer-wert, m. buffer value, -wirkung, /. buffer action or effect. 

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). 

The buffer range is the pH range over which the buffer is effective. It is related to the ratio of concentrations of the weak acid and its conjugate. The further the ratio is from 1, the less effective the buffering action. Ideally, the acid/base ratio should be between 0.1 and 10. Since log10 10 = 1 and log10 0.1 = — 1, buffers are most useful within 1 pH unit of the weak acid s pfQ. 

Scheme (b) includes reactions formerly described by a variety of names, such as dissociation, neutralisation, hydrolysis and buffer action (see below). One acid-base pair may involve the solvent (in water H30+ —H2OorH20 — OH ), showing that ions such as HsO+ and OH- are in principle only particular examples of an extended class of acids and bases though, of course, they do occupy a particularly important place in practice. It follows that the properties of an acid or base may be greatly influenced by the nature of the solvent employed. 

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... 

Coordinated phosphate control charts assume either that all contribution to pH level is derived from phosphate or that the buffering action of phosphate is sufficient to overcome the presence of other alkaline species, such as amines. Neither assumption is true. This may lead operators to conclude perhaps that a higher than anticipated bulk water pH level (caused by the presence of amine) should be rectified by the addition of MSP. This action may lower localized Na P04 ratios below 2.2 1.0, producing acid phosphate corrosion (phosphate wastage) and resulting in tube thinning and ultimately tube failure. 

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 ... 

Buffer action and complexation occur together in many natural settings. We conclude this chapter with a Box that describes one important example, the pH of soil. 

C18-0038. Write a paragraph that explains the chemical principles of buffer action. 

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. 

Measurement of free t-PA in plasma presents challenges in terms of preventing t-PA from complexing to PAI-1 released from platelets after blood collection. To dissociate any preformed t-PA-PAI-1 complex, the anticoagulant pH has to be close to 3.0. Even if blood is collected with an acidic anticoagulant, the blood pH will rise because of the powerful buffering action of hemoglobin. Thus, the pH of plasma has to be adjusted to 3.0 in order to dissociate the t-PA-PAI-I complex (115). 

The pyrophosphate buffer is of particular technical interest as it can be used over the relatively wide range of pH 3-9. Unlike the orthophosphate titration curve, that for the tetrabasic pyrophosphate system is almost straight [6]. This linearity (Figure 10.3) means that effective buffering action is available across the whole pH range simply by using various pairs of ionised components and varying their proportions even so, however, it does not seem to be widely used. 

Inactivation due to stomach acid. Prior to consumption of a meal, stomach pH is usually below 2.0. Although the buffering action of food can increase the pH to neutrality, the associated stimulation of stomach acid secretion subsequently reduces the ambient pH back down to 3.0-3.5. Virtually all biopharmaceuticals are acid labile and are inactivated at low pH values. 

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