Acid-base concepts Bronsted-Lowry theory

This concept covers most situations in the theory of AB cements. Cements based on aqueous solutions of phosphoric acid and poly(acrylic acid), and non-aqueous cements based on eugenol, alike fall within this definition. However, the theory does not, unfortunately, recognize salt formation as a criterion of an acid-base reaction, and the matrices of AB cements are conveniently described as salts. It is also uncertain whether it covers the metal oxide/metal halide or sulphate cements. Bare cations are not recognized as acids in the Bronsted-Lowry theory, but hydrated... 

The Bronsted-Lowry theory focuses on the transfer of a proton from one species to another. However, the concepts of acids and bases have a much wider significance than the transfer of protons. Even more substances can be classified as acids or bases under the definitions developed by G. N. Lewis ... 

Acid-Base Concepts The Bronsted-Lowry Theory 613... 

The acid-base concept, either in the limited interpretation of the Bronsted-Lowry theory or in the more general sense of the Lewis theory, is one of the most useful classification schemes in chemistry and a tool for systematizing the relationship between structure and reactivity. In this section we examine how this general concept can be applied to solid surfaces [29], From the most general (Lewis) point of view, a surface is classified as acidic (electron acceptor) or basic (electron donor) according to the direction of net electron transfer that results in the formation of new chemical bonds with an adsorbed molecule. 

This theory defines an acid as any compound that yields protons (H Ions) and a base as any compound that combines with a proton. In other words, acids are proton donors and bases are proton acceptors. It should be noted that as far as acids are concerned, Arrhenius and Bronsted - Lowry theories are similar in both cases acids give off ions. However, the concept of a base is much broader in the Bronsted theory, hydrorqrl ion being just one of the possible bases. Cited below are a few examples which wlU illustrate the point much better. 

Because of the aqueous environment of most biochemical reactions, the influence of ionization on the activity of biological compounds and the establishment of the pH scale, it is usual for the biochemist to consider acid and base behaviour in terms of the Bronsted and Lowry concept. According to the Bronsted-Lowry theory, an acid, HA, dissociates ... 

Bronsted-Lowry theory, which defines an acid as a proton donor, and a base as a proton acceptor. Utilizing this concept, a metal oxide (MO ) reacts with an acid (HA) ... 

Ideas about adds and bases (or alkalis) date back to ancient times. The word acid is derived from the Latin acidus (sour). Alkali (base) comes from the Arabic al-qali, referring to the ashes of certain plants from which alkaline substances can be extracted. The acid-base concept is a major theme in the history of chemistry. In this section, we emphasize the view proposed by Svante Arrhenius in 1884 but also introduce a more modern theory proposed in 1923 by Thomas Lowry and by Johannes Bronsted. 

Since Arrhenius, definitions have extended the scope of what we mean by acids and bases. These theories include the proton transfer definition of Bronsted-Lowry (Bronsted, 1923 Lowry, 1923a,b), the solvent system concept (Day Selbin, 1969), the Lux-Flood theory for oxide melts, the electron pair donor and acceptor definition of Lewis (1923, 1938) and the broad theory of Usanovich (1939). These theories are described in more detail below. 

It was G. N. Lewis who extended the definitions of acids and bases still further, the underlying concept being derived from the electronic theory of valence. It provided a much broader definition of acids and bases than that provided by the Lowry-Bronsted concept, as it furnished explanations not in terms of ionic reactions but in terms of bond formation. According to this theory, an acid is any species that is capable of accepting a pair of electrons to establish a coordinate bond, whilst a base is any species capable of donating a pair of electrons to form such a coordinate bond. A Lewis acid is an electron pair acceptor, while a Lewis base is an electron pair donor. These definitions of acids and bases fit the Lowry-Bronsted and Arrhenius theories, and cover many other substances which could not be classified as acids or bases in terms of proton transfer. 

Arrhenius in 1887 was the first person to give a definition of an acid and a base. According to him, an acid is one that gives rise to excess of in aqueous solution, whereas a base gives rise to excess of OH in solution. This was modified by Bronsted-Lowry in 1923 such that a proton donor was defined as an acid and a proton acceptor as a base. They also introduced the familiar concept of the conjugate acid-base pair. The final refinement to the acid-base theory was completed by Lewis in 1923, who extended the concept that acid is an acceptor of electron pairs while base is a donor of electron pairs. 

The concepts of acid-base equilibria were developed in this chapter for aqueous solutions (in aqueous solutions, water is the solvent and is intimately involved in the equilibria). However, the Bronsted-Lowry acid-base theory can be extended easily to other solvents. One such solvent that has been investigated in depth is liquid ammonia, NH3. 

The ability of certain chemical compounds to lose or gain protons has been an active area of research since the formulation the concept of pH in 1909 [1] and the appearance of the Bronsted-Lowry acid-base theory in 1923. According to Bron-sted and Lowry an acid is a compound that can donate a proton, whereas a base is a compound that can accept a proton. The dissociation of a proton from an acid in solution can be modeled by a simple equilibrium constant... 

In the year 1923, two more theories defining acid-base character were proposed. The first theory, Bronsted and Lowry theory, is very satisfactory for understanding physiological processes and will therefore form the basis of all further discussions. The second theory, proposed by G. N. Lewis is much more general than the Bronsted - Lowry concept. A brief discussion of this theory is given in Box 1.1. 

The addition of acid to the solution leads to shifts in the equilibria that favor the aqua-form of the complex. Thus, Pfeiffer, in 1906, established the reversible transformation of aqua-complexes into hydroxo-complexes. Werner later used this observation in the development of add-base concepts in coordination chemistry.32 Werner s work in this field is now largely of historical interest but two points, emphasized by Werner, remain espedally noteworthy, i.e. the importance of solvent in add-base equilibria and that bases may be considered as proton acceptors. These statements were incorporated into the acid-base theory developed by Bronsted and Lowry in 1923. 

The theory of Bronsted (1923) and Lowry (1923a, b) is of more general applicability to AB cements. Their definition of an acid as a substance that gives up a proton differs little from that of Arrhenius. However, the same is not true of their definition of a base as a substance capable of accepting protons which is far wider than that of Arrhenius, which is limited to hydroxides yielding hydroxide ions in aqueous solution. These concepts of Bronsted and Lowry can be defined by the simple equation (Finston Rychtman, 1982) ... 

Any text on acids and bases would not be deemed complete if mention were not made of the extended definition of acids and bases that is embodied in the Lowry-Bronsted theory. The theory basically proposed a more general definition of acids and bases to overpower the limitations of the theory arising from the Arrhenius concept. 

The concepts of the Lowry-Bronsted theory may explain the various reactions that take place during many non-aqueous titrations. Thus, an acid is a proton donor and a base is a proton acceptor. Therefore, when an acid HA undergoes dissociation it gives rise to a proton and the conjugate base A of the acid ... 

Bronsted and Lowry in 1923 gave proton exchange theory to explain the behaviour of acids and bases. According to this concept ... 

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