Weak acids buffered solutions

The electrolytic method is an indirect oxidation, as the small amount of bromide present is constantly converted to bromine, the actual oxidant. Essentially the reaction is the same as the action of bromine in weakly acidic buffered solution. The presence of only a small amount of extraneous salts is of advantage in processing the reaction mixture. The... 

Example 19-2 Weak Add/Salt of Weak Acid Buffer Solution (via the Henderson-Hasselbalch Equation)... 

In a weak acid buffer solution, when the concentrations of the weak acid and its conjugate base are equal the pH of the solution is equal to the pKa of the weak acid. 

Poly (butyl methacrylate, (2-dimethyl aminoethyl) methylacrylate) 1 2 1 R, R3= CH., r2 = CH2CH 2N(CH., r4 = ch c4H9 Eudragit E Cationic polymer. Soluble in gastric juices and weakly acidic buffer solutions pH 5. Film coalings. 

Min SK, Samaranayake CP, Sastry SK (2011) In situ measurements of reaction volume and calculation of pH of weak acid buffer solutions under high pressure. J Phys Chem B 115 6564-6571... 

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. 

In a perfectly-buffered solution the SO2 vapor pressure will be directly proportional to the total concentration of SO2 and bisulfite, giving a linear equilibrium relationship. In simple alkali sulfite solution without added buffer, the equilibrium relationship is highly nonlinear, because H-1" accumulates as SO2 is absorbed. Under these conditions is it not possible to carry out reversible SO2 absorption/stripping in a simple system, resulting in greater steam requirements than expected with a linear equilibrium relationship. Weak acid buffers such as sodium citrate have been proposed to "straighten" the equilibrium relationship and thereby reduce ultimate steam requirements (Jl, 2, 7). Citrate buffer is attractive because it is effective over a wide range, from pH 2.5 to pH 5.5 in concentrated solutions. 

It is expected that sodium citrate solution will behave as a typical weak acid buffer. Both solution pH and Ps02/pH20 should be independent of temperature. Under these conditions, the steam requirements will generally be independent of the stripper operating pressure and temperature (1, 2). 

An acidic buffer solution consists of a weak acid with a salt of the acid - its conjugate base. 

Buffer solutions are created by pairing a weak acid with a salt of its conjugate base or a base with a salt of its conjugate acid. Buffer solutions maintain a relatively stable pH when small amounts of acids or bases are added. 

An acidic buffer solution is made up of a weak acid HA and its salt (M+A ), where H denotes the presence in the molecule of hydrogen atoms which can form ions, and M+ refers to a (usually) metal ion ... 

Most buffer solutions are composed of a weak acid and one of its alkali salts. Usually such mixtures of an acid and its salt may be prepared to extend over a range of two pH units, between pK 1 and pK — 1 where pK is the negative logarithm of the dissociation constant Ka) of the acid. Buffer solutions made with acetic acid, which has a dissociation constant of 1.86 X 10 or a pK of 4.73, are useful in the pH range between 3.7 and 5.7. It should be recalled that the intensity of buffer action (buffer capacity) in a series of 0.7 buffer solutions is greatest in the mixture of pH equal to pK, in which the ratio of acid to salt is unity (cf. Fig. 13). The greater the difference between pH and pK, the less pronounced becomes the buffer action. A solution in which the acid to salt ratio exceeds 10 be stored unchanged. 

To the neutral or weakly acid sample solution in a 25-ml standard flask, containing not more than 12 pg of Co, add 2.5 ml of buffer solution, 2 ml of 5-Br-PADAP solution, water to -15 ml, and mix. After 15 min add 5 ml of 6 A/ H2SO4 and 1 ml of 0.01 M EDTA solution. Dilute to the mark with water, mix, and after 10 min measure the absorbance of the solution at 586 nm against a reagent blank solution. 

Put the weakly acidic sample solution, containing not more than 15 pg of Mn, into a separating funnel. Add 1 ml of 10% sodium-potassium tartrate solution and 1 ml of hydroxylamine solution, and dilute with water to 15 ml. Add 3 ml of buffer and 1 ml of PAN solution. After 2 min, shake the solution with chloroform for 1 min. Transfer the chloroform extract to a 25-ml standard flask and dilute to the mark with solvent. Measure the absorbance of the solution at 564 nm against a reagent blank. 

The most common preparation method for an acidic buffer solution is combining a weak acid with its conjugate base. The conjugate base comes from an aqueous salt which dissociates in water to give the base. A basic buffer solution can be prepared by combining a weak base with its conjugate acid. 

An alternative approach to making an acidic buffer solution is to start with a weak acid and add half as many moles of strong base. A basic buffer can also be prepared by starting with a weak base and adding half as many moles of strong acid. 

Eriochrome Cyanine R (C. I. Mordant Blue 3, Solochrome Cyanine R), a triphenylmethane dye, forms, in weakly acid solution, a violet lake with aluminum ions which is the basis of a spot test for the metal, One drop of the acidified sample is placed on a test plate and mixed with one drop each of Na acetate-acetic acid buffer solution (pH 5) and 1 % aqueous Eriochrome Cyanine R. The pH should be 4-6. One drop of NaHSOg solution is added. The formation of a violet color which is stable for 1 minute indicates the presence of aluminum. Iron i salts must first be reduced with ascorbic acid. Ti, Zr and Th ions form colored precipitates which must be centrifuged off. Cu must be masked with thioglycolic acid. 

Every buffer consists of a buffer pair. In most cases the components are a weak acid and its salt. To make a buffer solution, a weak acid in solution is mixed with a salt of its conjugate base (e.g. acetic acid and sodium acetate). The resultant chemical reactions in solution are shown in Table 1.2. Since the acid is weak, it only partially dissociates, as shown in reaction 1 of Table 1.2. The... 

Acidic buffer solutions may be prepared by mixing a weak acid, HA and a strong base, BOH, so that the following interaction occurs... 

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. 

Any solution containing comparable amounts of a weak acid, HA, and its conjugate weak base, A-, is a buffer. As we learned in Chapter 6, we can calculate the pH of a buffer using the Henderson-Hasselbalch equation. 

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