The Bronsted — Lowry Theory of Acids and Bases

Our initial definition of acids and bases in Section 3.3 involved the formation of hydronium ions (for acids) or hydroxide ions (for bases). This definition is attributed to Svante Arrhenius, but it can be expanded to include nonaqueous solutions, among other things. Formulated independently in 1923 by two chemists, Johannes Bronsted in Denmark and Thomas Lowry in England, the Bronsted-Lowry definition does just that. According to this definition, a Bronsted-Lowry acid is a proton (H+) donor, and a base is a proton acceptor. 

HCl has donated a proton to the water molecule, which accepted the proton, and we can write an equation to reflect this  

In the Bronsted-Lowry theory, a base is a proton acceptor. The OH (aq) ion produced by the ionization of NaOH(s) is a base because it can accept a proton from any proton donor  

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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. 

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. 

The Bronsted-Lowry definition of an acid is essentially the same as Arrhenius idea An acid is any substance that releases a hydrogen ion. Their idea has come to be known as the Bronsted-Lowry theory of acids and bases. 

Unlike the Arrhenius theory, the Bronsted-Lowry theory of acids and bases can explain the basic properties of ammonia when it dissolves in water. See Figure 8.4. 

These ideas were rather limiting since they only applied to aqueous solutions. There were situations where acid-base reactions were taking place in solvents other than water, or even in no solvent at all. This problem was addressed in 1923 by the Danish chemist Johannes Bronsted (1879-1947) and the English chemist Thomas Lowry (1874-1936) when they independentiy proposed a more general definition of acids and bases, and the study of acids and bases took a great step forward. This theory became known as the Bronsted-Lowry theory of acids and bases. 

Describe the Bronsted-Lowry theory of acids and bases... 

The Bronsted-Lowry Theory of Acids and Bases The Role of Water in the Brensted-Lowry Theory Weak Acids and Bases... 

According to the Bronsted-Lowry theory of acids and bases, an acid is a proton donor and a base is a proton acceptor. The proton, which in this context means a hydrogen ion, H , is highly mobile and acids and bases in water are always in equihbrium with their deprotonated and protonated counterparts and hydro-nimn ions (H3O , 8). Thus, an acid HA, such as HCN, immediately estabhshes the equihbrium... 

In a reaction at equilibrium, products are being converted to reactants at the same rate as reactants are being converted to products. The reverse reaction can also be considered in terms of the Bronsted-Lowry theory of acids and bases. 

Johannes Nicolaus Bronsted and Thomas Martin Lowry simultaneously developed the proton donor/acceptor theory of acids and bases in the... 

In 1923, two chemists working independently of each other, proposed a new theory of acids and bases. (See Figure 10.4.) Johannes Bronsted in Copenhagen, Denmark, and Thomas Lowry in London, England, proposed what is called the Brpnsted-Lowry theory of acids and bases. This theory overcame the problems related to the Arrhenius theory. 

Bronsted-Lowry theory of acids and bases the theory defining an acid as a substance from which a hydrogen ion can be removed and a base as a substance that can remove a hydrogen ion from an acid (10.1)... 

NHj contains no hydroxide ions yet when you put it in water it increases the hydroxide ion concentration. To account for examples such as this we have what is known as the Bronsted-Lowry (Johannes Bronsted and Thomas Lowry) theory of acids and bases. In this definition an acid is any substance that donates protons in a reaction and a base is any substance that accepts protons in a reaction. This is basically (no pun intended) the same as the Arrhenius definition of acids because if a substance readily donates protons in a reaction it will also increase the hydronium ion concentration when placed in water. The definition of a base, though, is expanded to include any substance that readily accepts protons in a reaction, and that substance doesn t have to contain hydroxide ions. Let s continue with our above example. There, NH contributed to the Off concentration when dissolved in water. But NH3 is also a proton acceptor (which we have defined as a base) because it picks up a proton to become as in... 

Just after the First World War in 1923, Bronsted and Bjerrum in Denmark and Lowry in Great Britain jointly put forward a more acceptable and satisfactory theory of acids and bases which is devoid of objections earlier raised in Arrhenius definition. 

The limitations of the Arrhenius theory of acids and bases are overcome by a more general theory, called the Bronsted-Lowry theory. This theory was proposed independently, in 1923, by Johannes Br0nsted, a Danish chemist, and Thomas Lowry, an English chemist. It recognizes an acid-base reaction as a chemical equilibrium, having both a forward reaction and a reverse reaction that involve the transfer of a proton. The Bronsted-Lowry theory defines acids and bases as follows ... 

The Arrhenius theory accounts for the properties of many common acids and bases, but it has important limitations. For one thing, the Arrhenius theory is restricted to aqueous solutions for another, it doesn t account for the basicity of substances like ammonia (NH3) that don t contain OH groups. In 1923, a more general theory of acids and bases was proposed independently by the Danish chemist Johannes Bronsted and the English chemist Thomas Lowry. According to the Bronsted-Lowry theory, an acid is any substance (molecule or ion) that can transfer a proton (H + ion) to another substance, and a base is any substance that can accept a proton. In short, acids are proton donors, bases are proton acceptors, and acid-base reactions are proton-transfer reactions ... 

The Lewis theory of acids and bases is more general than Bronsted-Lowry theory, but Bronsted-Lowry s definition is used more frequently. The terms "acid" and "base" most often refer to Bronsted acids and bases, and the term "Lewis acid" is usually reserved for chemicals like BF3 that are not Bronsted acids. 

Bronsted acid-base theory — In 1923, Bron-sted and, independently of him, Lowry published essentially the same theory of acids and bases which can be applied not only to water as a solvent but also to all other - protic solvents, as well as to proton transfer reactions in gases. An acid is defined as a proton donor, i.e.,... 

Acids are compounds that ionise to release hydrogen ions, or protons, to their surroundings. Bases are compounds that can accept hydrogen ions. This is called the Bransted-Lowry definition of acids and bases (named after yet another Scandinavian chemist, Johannes Nicolaus Bronsted, and Thomas Martin Lowry, who was British). There are other ways of explaining acidity and basicity, but the Bransted-Lowry theory works most of the time, and will be used throughout this book. 

The theory of acids and bases, the Bronsted-Lowry theory, was dependent on the presence of proton (H ) to show acidic or basic properties, which may not always be the case hence in 1923, G. N. Lewis introduced a theory of acids and bases with a more general definition of acid-base reactions by examining what happens when an ion combines with an OH ion to form water. 

There are various definitions of acids and bases. The one used here is attributed to a theory developed in 1923 independently by Johannes Bronsted (1879-1947), a Danish chemist, and Thomas Lowry (1874-1936), a British chemist. Recall that an atom of ordinary hydrogen has only a proton and an electron, and no neutrons. Therefore, a cation of ordinary hydrogen (H+) is just a proton. In the Bronsted-Lowry definition of acids and bases, an acid is a proton donor, that is, it can react with other compounds or ions by transferring one or more ions to the other compounds or ions. A base is a proton acceptor It can react with the H+ ions of compounds or ions that are acids. Some chemical species, such as H O, are said to be amphiprotic, that is, they are both donors and acceptors of protons they are both an acid and a base. These definitions are illustrated in the following examples ( aq means the reaction is taking place in aqueous solution) ... 

The first complete theory of acids and bases was formulated by Arrhenius in 1897 (124) in water, acids dissociate to produce H, whereas bases produce OH . The more advanced and general Bronsted—Lowry theory was proposed in 1923 (125,126). According to this theory, acids are substances able... 

The Lewis Theory of acids and bases does not feature the special role for the proton that it has in the Bronsted-Lowry theory. Here an acid is any electron-pair deficient species. A base from this viewpoint is a species capable of furnishing electron pairs. Thus, acid-base reactions are considered as coordination reactions. This theory is of great value in understanding metal coordination complex formation. 

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... 

These definitions are sufficiently broad that any hydrogen-containing molecule or ion capable of releasing a proton, H, is an acid, whereas any molecule or ion that can accept a proton is a base. In the Arrhenius theory of acids and bases, only substances that contain the OH group would be called bases. The Bronsted-Lowry theory expands the definition of bases to include substances that have one or more lone pairs of electrons that can act as proton acceptors. 

A (a) Give an example of a substance that is an acid and one that is a base, according to the Arrhenius theory of acids and bases, (b) Give an example of a Bronsted-Lowry acid that is not an Arrhenius acid, (c) Give an example of a Brunsted-Lowry base that is not an Arrhenius base. 

Johannes Nicolaus Brdnsted (1879-1947). Danish chemist. In addition to his theory of acids and bases, Br0nsted worked on thermodynamics and the separation of mercury into its isotopes. In some books. Brpnsted acids and bases are called Bronsted-Lowry acids and bases. Thomas Martin Lowry (1874—1936). English chemist. Brpnsted and Lowry developed essentially the same acid-base theory independently in 1923. 

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