Acid-base concepts relevance

The subject is also closely related to fuel-ash corrosion which in most cases is caused by a layer of fused salts such as sulphates and chlorides Attention has been focused on the electrochemistry of this type of corrosion and the relevant thermodynamic data summarised in the form of diagrams . Fluxing and descaling reactions also resemble in some respects reactions occurring during the corrosion of metals in fused salts. A review of some of the more basic concepts underlying corrosion by fused salts (such as acid-base concepts and corrosion diagrams) has appeared. ... 

The scope of the reviewed R D work is limited to intermediate-T acid-base blend membranes prepared by mixing polybenzimidazoles and sulfonated or phosphonated acidic polymers. Other membrane types, where the acid-base concept was used to improve their relevant... 

The concept of acid-base interaction is often used in the physics of adhesion to account for the formation of interfacial bonds, in heterogeneous catalysis to analyze the reactivity and selectivity of solid catalysts, and in colloid physics to describe the double-layer interactions between small particles in suspension in a liquid. This chapter will present a brief historical sketch of the acid-base concept in molecular physics and will specify its relevance in adhesion and catalysis. Then, the acid-base characteristics of oxide surfaces will be described, with special attention paid to the properties of hydroxyl groups on these surfaces. 

Yokoyama and coworkers investigated the discolouration of titanylphthalocyanine 60, and related porphyrins by silyl radicals derived from methylphenylpolysilane by molecular orbital methods60. Calculated values of AN, the index derived from the hard and soft acids and bases concept was determined from HF/3-21G calculated ionization potentials, electron affinities, and HOMO and LUMO orbital energies of the systems of interest. These studies predict that PhMe2Si should donate an electron readily to 60 to form 60 (equation 18). This prediction is of direct relevance to observations that irradiation of titanylphthalocyanine-coated methylphenylpolysilane films leads to discolouration of the film60. 

Central to the stability and chemistry of complexes formed by mixed donor ligands are two key concepts of coordination chemistry. The first is the chelate effect, which applies to all polydentate ligands, and reflects the increase in stability of a type of complex as monodentate donor molecnles are replaced by polydentates with donors linked by chelate rings. The hard-soft acid-base theory is particnlarly relevant to mixed donor ligands where donors of distinctly different character may bind to a central metal ion. The like prefers like concept means hard nonpolarizable donor atoms (N and O, for example) bond preferentially to hard nonpolarizable metal... 

Sketch an Eh-pH plot for the S-H2O-O2 system, and comment on the relevance of kinetic versus equilibrium concepts and of microorganisms in facilitating the acid-base and redox reactions described by boundaries on the diagram. 

Recently, much attention is being placed on fibres-reinforced/polymer systems as subjects of study. It was caused by increasing emphasis on high performance reinforced polymer composites. The concept of acid/base interactions across the fibre/polymer interface was noted particularly and the relevance of acid/base theories to the behaviour of po-... 

Louis P. Hammett (1894-1987) made two major contributions to physical-organic chemistry the first one (on which wc will focus) is the concept of supcracidity and his acidity function. The. second one is the so-called llammeti equation wiiich concents the correlation of equilibria and rales for reactions of substituted aromatic compounds. With A.H. Deynip. Hammett set up an acidity scale based on the indicator properties of aromatic amines, a. scale that measures 100% sulfuric acid as lo limes as strong as 10% acid, and then showed that this acidity scale was relevant to chemisir> ... 

In between these limiting cases, compromises are possible, but they should be explained. As examples, one might wish to apply a mechanistic model to a sorbent, for which the acid-base properties can for some reason (e.g., the dominating crystal planes are not known) not be described in such detail as is, for example, possible for well-crystaUized goethite. In such cases, the features, which are known to be relevant, should be included to such an extent that adjustable parameters are limited to the number, which is actually necessary to accurately describe the experimental data. In particular, the acid-base properties are important in deciding on the basic model concept. Therefore, the simplest model for the accurate description of acid-base properties accounting for electrolyte specific behavior (e.g. 1-pK, single site. Stem model) would be appropriate, which can be extended with many options to the description of solute adsorption. 

Among the various strategies [34] used for designing enantioselective heterogeneous catalysts, the modification of metal surfaces by chiral auxiliaries (modifiers) is an attractive concept. However, only two efficient and technically relevant enantioselective processes based on this principle have been reported so far the hydrogenation of functionalized p-ketoesters and 2-alkanons with nickel catalysts modified by tartaric acid [35], and the hydrogenation of a-ketoesters on platinum using cinchona alk oids [36] as chiral modifiers (scheme 1). 

The ABC activities provide a meaningful way for students to learn new concepts. The activities are specifically designed to create in the students a sense that the topics under discussion represent concepts that they need to know. As Veronica and Leroy explore water uses in their community, they discover (with the help of their teacher) that they cannot complete their research without learning about acids and bases, new concepts (for them) to which they had never given serious thought. This discovery initiates a series of activities designed to help students understand the usefulness of information about acids and bases and other relevant concepts. In one activity, the students perform inventories of the acid content and characteristics of the foods in their... 

Because of the real-life context that introduces the laboratory, students see the importance of the key concepts involved in adjusting the pH. To ensure that students see that this is but one of many contexts in which the ability to adjust pH is relevant, the Water subunit on acids and bases includes (under Activities by Occupational Area ) additional activities in which students are introduced to real-life applications in five broad categories ... 

To emphasize the concept of base strength, consider the basic properties of the cyanide ion. One relevant reaction is the dissociation of hydrocyanic acid in water ... 

The two main threads of recent research on ion channels—investigations of channel structure and channel function—are interrelated in that research in each area illuminates both. Biologists realize that an understanding of function must be based on structure, but it has been difficult to extract clues relevant to function from the very detailed information about amino acid sequences and their arrangements in the channel proteins. This is where the concepts of electrochemistry have proven useful. Consideration of average properties and large populations of channels, rather than specific groups in an individual channel (the focus of much current research), has made it possible... 

Finally, the new concept of DNA-based asymmetric catalysis in which DNA serves as a chiral scaffold for catalyst design was described. To date, DNA-based asymmetric catalysis has been applied successfully to Lewis acid catalyzed reactions in water. This concept shows much promise for application in organic synthesis as it is inexpensive, experimentally straightforward, can be performed at a synthetically relevant scale, and the catalyst can be recycled readily. 

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