Acid-base constants

The value of AH can be calculated from the acid-base constants of the interacting phases by using the theory of Drago [38] or Guttman [39]. Drago [38] suggested two constants for each material and divided the compounds into acids and bases. AH can be calculated as ... 

Equation 24 is derived from the Young (Eq. 21), the Dupre (Eq. 8) and the Eowkes (Eq. 10) equations by assuming complete wetting (cos 0 =0). Measurements with polar solvents give the polar component of the surface tension, but acid/base constants and the corresponding work of adhesion can also be calculated from them ... 

D. Sykora, E. Tesarova, and D. W. Armstrong, Practical Considerations of the Influence of Organic Modifiers on the Ionization of Analytes and Buffers in Reversed-Phase LC, LCGC 2002,20, 974 G. W. Tindall, Mobile-Phase Buffers. I. The Interpretation of pH in Partially Aqueous Mobile Phases, LCGC 2002,20, 102 S. Espinosa, E. Bosch, and M. Roses, Acid-Base Constants of Neutral Bases in Acetonitrile-Water Mixtures, Anal. Chim. Acta 2002,454, 157. 

S. Espinosa, E. Bosch, and M. Roses, Acid-base constants of neutral bases in acetonitrile-water mixtures, A aZ. Chim. Acta 454 (2002), 157-166. 

The molar fractions of oxo (thiono) and hydroxy (thiol) tautomers for a series of monohydroxy- and monomercapto-substituted pyridines, quinolines, and acridines were calculated from the acid-base constants of these compounds at the isoelectric points in an amphiphilic medium (80ZOR1499). 

From the known values of the acid-base constants for vanadium oxocompounds one can establish the relationship between different acid-base forms in the studied chloride melt over a wide range of pO. The corresponding dependence is presented in Fig. 1.2.9b. It is seen that in the case of Vv oxo-compounds more than two acid-base forms can coexist in a relatively wide pO range, which gives rise to additional errors in the equilibrium constant calculations. Nevertheless, in the given case this does not lead to an appreciable directed shift of the calculated values of the equilibrium constants, or to an increase of the confidence ranges for reactions (1.2.86) and (1.2.87). 

Unstable chemical systems, which cannot be Investigated by many other techniques, can be conveniently studied by FIA. Thus, determinations Involving reagents liable to be affected by contact with the atmosphere (e.g. strong reductants [77,78]) or systems yielding unstable monitored products [60] pose hardly any problem when carried out by FIA, which Is also an Invaluable tool for the determination of acid-base constants of easily hydrolysable substances [90]. 

Tencheva J, Velinov, G and Budevsky O, New approach of the extrapolation procedure in the determination of acid-base constants of poorly soluble pharmaceuticals. Arzneim.-Forsch., 29, 1331-1334 (1979). Cited in Lombardo F, Obach RS, Shalaeva MY and Gao F, Prediction of human volume of distribution values for neutral and basic drugs. 2. Extended data set and leave-class-out statistics, J. Med. Chem., 47,1242-1250 (2004) ref. 284. 

Rank the following aqueous solutions in order of increasing pH (you will need to refer to a table of acid/base constants). Explain your reasoning. 

Table 1. acid-base constants in water and the alcohols... 

Below are collected some acid-base constants, pK , the negative log of the acidity (dissociation) constant. See Chapter 5 for definitions and forms. First, the pK° values are given, followed by the conditional values at 25° and 0.1 M ionic strength, unless other conditions are stated. 

Acid-base constants from OO peak shifte... 

Acid-base constant from OH peak shifts... 

Acid-base constants/proton-affinity constants These parameters cannot, at present, be established experimentally. Because there are probably several distinct sites and electrostatic effects, the overall surface-charge curves do not give any hint as to the nature and reactivity of these sites. Experimental back-titration data by Schulthess and Sparks [103], which indicate steps in the proton adsorption isotherm (i.e., the surface-charge density versus pH curve), were interpreted by these authors to be indicative of individual sites with individual reactivities. However, such data are not reproduced by the bulk of research groups. In the previous subsection, the back-titration technique has been discussed in some detail and, in particular, the results on goethite obtained with base titrations at low pH were found to show significant scatter compared to data obtained with the coulometric approach. 

In the fiumework of realistic surface complexation models (realistic in the sense of realistically accounting for expected features), site densities are known for well-defined sorbent samples. For natural sorbent samples and powders, this is not the case. Realistic acid-base constants for such sorbent samples are difficult to obtain. Spline analysis of proton consumption functions or numerically fitting a model to such sorbents are presently the preferred approaches. However, they involve the respective assumptions, and reahstic models await improved experimental (most probably spectroscopic) methods to define the amount and nature of surface sites. Otherwise, in generic models, acid-base constants are model-dependent parameters, which have some use when apphed self-consistently, but should not be interpreted as realistic parameters. This is a very controversial statement, which is in conflict with many modeling studies in which generic models of the surface acid-base properties are combined with spectroscopic information on sorbing ions. 

One may define a constant x analogous to the acid-base constants Ka. Let s consider, for example, the reaction... 

Ca, Cb Drago s acid base constants AES Auger electron spectroscopy... 

Ea, Eb Drago s acid base constants DRIFT Diffuse reflectance infrared... 

Young s or tensile modulus of the substrate acid-base constants applied force or load... 

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