Aqueous equilibria acid-base titrations

Since there was no direct reaction of CO with the chloride melt, its concentration in the gas mixture was neglected and corrections for the partial pressure of C02 were not made. The melt was analyzed periodically for this purpose, several samples were taken off the melt, dissolved in water, and subjected to acid-base titration in aqueous solution, to determine the ratio of concentrations of Na20 to Na2C03 as described above. These studies provided the temperature dependences of the equilibrium constant of (1.2.3) in four melts of the KCl-NaCl system in the 1 temperature range 1025 -1125 K, as follows ... 

NO2, or OEt] The best results were obtained with a 40 15 hexane-ethyl acetate mixture. The values were determined for the acid-base equilibrium of A -(2-benzothiazolyl)succinamic acid (202) by potentiometric titration in 60% aqueous dioxan and 50% ethanol. ... 

Metrohm markets microprocessor-controlled Instruments for routine coulo-metric (KF 652 Processor) and amperometrlc-voltammetrlc (EP/KF 678 Processor) analyses. These Instruments are frequently used for research purposes. Thus, the Mettler Memotltrator and the Metrohm Tltroprocessor 636/Rod Stirrer 622 were used by Johansson et al. [62] to demonstrate that potentiometric two-phase titrations can be carried out in an automatic fashion. The typical background noise from the electrodes can be reduced by Introducing hydrophobic anions or cations in the aqueous phase. These ions also affect the acid-base equilibrium by extracting the sample ions as ion-pairs into the organic phase, which allows the conditional acidity constant (apparent K ) to be manipulated to make selective titrations possible. 

Etingov ED and Kholodova GV, Kul bakh VO and Kamatushkina AI, Acid-base properties of amphotericin B, Antibiotiki, 17, 301-305 (1972). "Titration of 66% aqueous dimethylformamide solutions of Amphotericin B with methanolic HCl and KOH yields pK s near 5.7 and 10.0. Comparison with N-acetyl-Amphotericin B (pK=6.5) and Amphotericin B-methyl ester (pK=8.8) assigns the two pK s to carboxyl and amino groups respectively. Amphotericin B is found to be almost completely zwitterionic in this solution (tautomeric equilibrium constant Kt = 1000 with respect to the neutral molecule)." S R... 

In this chapter we will continue the study of acid-base reactions with a discussion of buffer action and titrations. We will also look at another type of aqueous equilibrium—that between slightly soluble compounds and their ions in solution. 

In the discussion of the relative acidity of carboxylic acids in Chapter 1, the thermodynamic acidity, expressed as the acid dissociation constant, was taken as the measure of acidity. It is straightforward to determine dissociation constants of such adds in aqueous solution by measurement of the titration curve with a pH-sensitive electrode (pH meter). Determination of the acidity of carbon acids is more difficult. Because most are very weak acids, very strong bases are required to cause deprotonation. Water and alcohols are far more acidic than most hydrocarbons and are unsuitable solvents for generation of hydrocarbon anions. Any strong base will deprotonate the solvent rather than the hydrocarbon. For synthetic purposes, aprotic solvents such as ether, tetrahydrofuran (THF), and dimethoxyethane (DME) are used, but for equilibrium measurements solvents that promote dissociation of ion pairs and ion clusters are preferred. Weakly acidic solvents such as DMSO and cyclohexylamine are used in the preparation of strongly basic carbanions. The high polarity and cation-solvating ability of DMSO facilitate dissociation... 

It is, however, more likely that the discrepancies observed in the periodate oxidation of malonaldehyde concern mainly the hydroxylation step. In the mechanism proposed (5) for this reaction, it is the enol form of malonaldehyde which is hydroxylated. However, titrations of a solution of malonaldehyde, prepared by hydrolysis of an aqueous solution (33) of carefully distilled 1, 3, 3-tri-ethoxypropene (46, 47), both with strong base and with iodine, indicate that only about 80% of the enol form is present in the equilibrium solution. On the other hand, the thio-barbituric acid test (58, 59) gave consistently higher values for the malonaldehyde content of the solution. The fact that only about 80% of the enol form is present in the equilibrium solution is all the more important as it can be shown (56) by titration with strong base that the enolization is slow, and moreover does not seem to go to completion. 

Firstly, ion exchange resins when hydrated generally dissociate to yield equivalent amounts of oppositely charged ions. Secondly, as with conventional aqueous acid or alkali solutions, resins in their acid or base forms may be neutralized to give the appropriate salt form. Finally, the degree of dissociation can be expressed in the form of an apparent equilibrium constant (or pK value) which defines the electrolyte strength of the exchanger and is usually derived from a theoretical treatment of pH titration curves. ... 

Results from [3043] were cited in [1], and then quoted after [1] in numerous papers. Inspection of the original paper reveals that the quality of pristine PZCs/ lEPs derived from the results presented in [3043] is limited. Table 1 reports equilibrium pH of aqueous suspensions of four oxides, apparently containing occluded acid or base and/or multivalent ions. Eigure 1 shows a titration curve with no data points between pH 5 and 9. Eigure 2 shows uptake of monovalent ions by two oxides as a function of pH. The uptake is not a monotonic function of pH, and there are very few data points in the vicinity of the PZC. ... 

In aqueous solutions the principles of analytical chemistry established the protocol to use strong acids (or bases) as titrants they "see" all bases (or acids) in the system, and the result of titration is a "total basicity" (or "acidity") number. If an additional method to measure the concentration of "free" acid at different titration points and under equilibrium conditions were available, then one could use aqueous titration methods to isolate bases (or acids) of different strengths that might be present in the system and evaluate their amount. 

Nonaqueous titrations are frequently desirable or required because of the increased sensitivity, improved selectivity, or greater solubility achieved with nonaqueous solvents. A far greater number of acids and bases can be determined in nonaqueous solvents than in aqueous media. This is primarily true because of the numerous organic acids and bases that require organic solvents. Properties such as dissolving or solvating, diffusion or equilibrium constants, acidity or basicity, and dielectric constant or polarity extend the capability of titrimetry to a far wider range when nonaqueous solvents are used. 

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