Determination of acidic and basic

Very widespread for precise routine and non-routine analysis in industrial and research laboratories. Typical uses determination of acidic and basic impurities in finished products, control of reaction conditions in industrial processes, mineral and metallurgical analysis. Relative precision 0.1-1%. 

In practice, experimental determinations of acidity and basicity are rarely if ever absolute ... 

Fraenkel-Conrat, H. and Cooper M.J, 1944. The use of dyes for the determination of acid and basic groups in proteins. J. Biol. Chem. 154, 239-246. 

Cappiello, A., Famiglini, G., and Bruner, F., Determination of acidic and basic/neutral pesticides in water with a new microliter flow rate LC/MS particle heam interface. Anal. Chem., 66, 1416-1423, 1994. 

Determination of Acidic and Basic Properties on Solid Surfaces... 

Karasek et al. [1] determined hydrocarbons in benzene water extracts (pH7) of soil and in incinerator or fly ash by a variety of techniques including gas chromatography with flame ionization, electron capture and mass spectrometric detectors. Benzene water extractants were adjusted to pH4, 7 and 10 before the extraction in order to selectively extract various types of acidic and basic organic compounds in addition to hydrocarbons. 

It was proven that microcalorimetry technique is quite well developed and very useful in providing information on the strength and distribution of acidic and basic sites of catalysts. When interpreting calorimetric data, caution needs to be exercised. In general, one must be careful to determine if the experiments are conducted under such conditions that equilibration between the probe molecules and the adsorption sites can be attained. By itself, calorimetry only provides heats of interaction. It does not provide any information about the molecular nature of the species involved. Therefore, other complementary techniques should be used to help interpreting the calorimetric data. For example, IR spectroscopy needs to be used to determine whether a basic probe molecule adsorbs on a Brpnsted or Lewis acid site. 

Rony called catalysis of the type illustrated in Eq. 9-93 tautomeric catalysis and suggested that its efficiency lies not simply in the close proximity of acidic and basic groups in the same molecule but also in the ability of the catalyst to repeatedly cycle between the two tautomeric states.133 For an enzyme the tautomer-ization of the free catalyst could sometimes be rate determining (see Section A,4 on isomechanisms). 

The mechanism of an enzymatic reaction is ultimately defined when all the intermediates, complexes, and conformational states of the enzyme are characterized and the rate constants for their interconversion are determined. The task of the kineticist in this elucidation is to detect the number and sequence of these intermediates and processes, define their approximate nature (that is, whether covalent intermediates are formed or conformational changes occur), measure the rate constants, and, from studying pH dependence, search for the participation of acidic and basic groups. The chemist seeks to identify the chemical nature of the intermediates, by what chemical paths they form and decay, and the types of catalysis that are involved. These results can then be combined with those from x-ray diffraction and NMR studies and calculations by theoretical chemists to give a complete description of the mechanism. 

The diverse types of oxygen functional groups determine the acidic and basic character of the carbon surfaces [175,182], The acidic character is typically linked with surface complexes like carboxyl, lactone, and phenol, while the basic nature is regularly assigned to surface groups, such as pyrone, ether, and carbonyl [173,178] (see Figure 2.32). 

K Tanabe Solid Acid and Base Catalysts This chapter deals with the types of solid acids and bases, the acidic and basic properties, and the structure ofacidic and basic sites. The chemical principles of the determination of acid-base properties and the mechanism for the generation of acidity and basicity are also described. Howacidid and basic properties are controlled chemically is discussed in connection with the preparation method of solid acids and bases. 

Quantitative information on the number of sites may be obtained from a volumetric or gravimetric study of the adsorption of oxidizing or reducting molecules. Adsorption calorimetry can be used to determine the energetics of the site distribution, as in the case of acidic and basic sites. 

Since the amide backbone of a protein is neutral and uncharged, the isoelectric point of a protein or peptide is determined by the relative numbers of acidic and basic amino acid residues present in the peptide. 

K, and d = 1 nm at several values of the electrolyte concentration n. We see that the surface potential i/iq and its lEP (i.e., the intersection of each curve with the i/iq = 0 axis) vary with the electrolyte concentration n. For comparison, the corresponding results for a soft surface with uniform distribution of acidic and basic groups are given in Fig. 4.9, which shows that all intersections of curves calculated for different electrolyte concentrations with the i/iq = 0 axis are the same. In other words, the lEP of a uniformly charged soft surface is independent of the electrolyte concentration. The dependence of the surface potential i/iq on the electrolyte concentration corresponds to the following fact. The surface potential is determined by the... 

From the Hterature it is apparent that microcalorimetry is very useful in providing informahon on the strength and distribution of acidic and basic sites of catalysts. The technique for determining the acid site distribution is quite well developed, especially if ammonia is used as the basic probe molecule. Moreover, the energehcs of surface reachons, including oxidahon and reduction of metal oxides, oxidahon of adsorbed hydrocarbons or hydrogen and decomposihon reachons can be determined direchy by calorimehy [4]. 

As before, these relative acidities are determined b, displacement (Sec. 8.10). We may expand our series of acidities and basicities, then, to the following ... 

For an acid titrated halfway to its equivalent point, pH = pKa. For mixtures of acids and bases, and hence for carbons having functional groups of different acid or basic strength, this holds true as well. For weak acid and base groups, the effect of water dissociation is significant around pH = 7. Therefore, a simple potentiometric titration can give information about the dissociation constants and neutralization equivalence of the carbon. In several cases these indications can be sufficient to determine the nature of the functional groups and provide a comprehensive description of the behavior of carbon in terms of acidity and basicity. A differential plot of the titration curve can be considered in the same way as a conventional absorption spectrum of the sample. Acidity or basicity constants are then calculated at half-titration, as pH = pKw — pKb for a base and pH = pKa for an acid. 

Stoichiometry provides the basis for a procedure called titration, which is used to determine the concentrations of acidic and basic solutions. Titration is a method for determining the concentration of a solution by reacting a known volume of the solution with a solution of known concentration. If you wished to find the concentration of an acid solution, you would titrate the acid solution with a solution of a base of known concentration. You also could titrate a base of unknown concentration with an acid of known concentration. How is an acid-base titration carried out Figure 19-16 illustrates the equipment used for the following titration procedure using a pH meter. 

---