Acids Bronsted-Lowry theory

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 Lowry-Bronsted theory suffers from the following drawbacks (i) it explains the acidic or the basic nature of a substance only if a solvent such as water is present. In other words, molecules such as HC1, H2S04, etc. are not acids in the absence of water (ii) this concept fails to explain how acidic oxides (such as C02, S02, etc.) are neutralized by basic oxides (such as CaO, BaO) since there is no involvement of protons in these reactions, e.g. ... 

The Lowry-Bronsted theory says an acid is a proton donor. 

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 ... 

According to the Lowry-Bronsted theory of acids and bases, an acid is a substance which... 

In the Lowry-Bronsted theory of acids and bases (1923), the definition was extended to one in which an acid is a proton donor, and abase is a proton acceptor. For example, in... 

The original Arrhenius definition of a base has been extended by the Lowry-Bronsted theory and by the Lewis theory. See acid. 

In 1923 the Arrhenius idea of adds and bases was extended by the British chemist Thomas Martin Lowry (1874-1936) and, independently, by the Danish physical chemist Johannes Nicolaus Bronsted (1879-1947). In the Lowry-Bronsted theory an acid is a compound that can donate a proton and a base is a compound that can accept a proton. Proton donators are called Bronsted acids (or protic acids) and proton acceptors are called Bronsted bases. For example, in the reaction ... 

One important aspect of the Lowry-Bronsted theory is that, because it involves proton transfers, it does not necessarily have to involve water. It is possible to describe reactions in nonaqueous solvents, such as liquid ammonia, in terms of acid-base reactions. 

All references to the free proton of hydrogen ion should be avoided. The Lowry-Bronsted theory should be relegated to a historical survey unconnected with the teaching of first principles. In this connection, I recommend a detailed scrutiny of G. N. Lewis paper of 1938, coming as it does after the establishment of the quantum-wave mechanical theory of valence. In that paper he was able to look back at his book of 1923. He pointed out that in aqueous solutions only a small part of the range of acid and basic strengths can be studied. His assessment of Bronsted s conclusions should be noticed. 

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. 

If baking soda is added to hydrochloric acid, however, it does accept a hydrogen ion. So, according to Bronsted and Lowry s theories, baking soda is a base ... 

Brensted-Lowry theory chem A theory that all acid-base reactions consist simply of the transfer of a proton from one base to another. Also known as Bronsted theory. ( jbran steth lau re, the-3-re ... 

Bronsted-Lowry A theory that defines an acid as a proton donor, and a base as a proton acceptor. 

Lowry s theory that the substrate is attacked simultaneously by acids and bases leads to a variety of possibilities of hydroxide ion and hydrogen ion catalysis in aqueous solution according to the values of Xa and Xb in Bronsted s equations. With Xb large and Xa very small, the reaction is catalyzed by base but not by acid with Xa large and Xb very small, the reaction is catalyzed by acid but not by base with Xa and Xb of intermediate magnitudes, the reaction is catalyzed by both acids and bases and with both Xa and Xb either very large or very small, the reaction is not apparently faster in the presence of either acids or bases. 

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 mentioned leveling effect of the solvent (or excess acid itself acting as such) the acidity cannot exceed that of its conjugate acid. In the case of water the limiting acidity is that of HsO. Proton-ated water, H30 (hydronium ion), was first postulated in 1907, and its preeminent role in acid-catalyzed reactions in aqueous media was first realized in the acid-base theory of Bronsted and Lowry. Direct experimental evidence for the hydronium ion in solution and in the... 

This more general view of acids and bases is named the Bronsted-Lowry theory after the two scientists who proposed it, J. N. Brpnsted and T. M. Lowry. 

The Bronsted-Lowry theory of acids and bases referred to in Section 10.7 can be applied equally well to reactions occurring during acid-base titrations in non-aqueous solvents. This is because their approach considers an acid as any substance which will tend to donate a proton, and a base as a substance which will accept a proton. Substances which give poor end points due to being weak acids or bases in aqueous solution will frequently give far more satisfactory end points when titrations are carried out in non-aqueous media. An additional advantage is that many substances which are insoluble in water are sufficiently soluble in organic solvents to permit their titration in these non-aqueous media. 

In the Bronsted-Lowry theory, any acid (HB) is considered to dissociate in solution to give a proton (H + ) and a conjugate base (B ) whilst any base (B) will combine with a proton to produce a conjugate acid (HB + ). 

Acids Bronsted-Lowry theory of, 21 common, concentration of, (T) 829 dissociation constants of, (T) 832 hard. 54 ionisation of, 20 Lewis, 22 polyprotic, 20... 

The term proton in these definitions refers to the hydrogen ion, H+. An acid is a species containing an acidic hydrogen atom, which is a hydrogen atom that can be transferred as its nucleus, a proton, to another species acting as a base. The same definitions were proposed independently by the English chemist Thomas Lowry, and the theory based on them is called the Bronsted-Lowry theory of acids and bases. 

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