Bronsted-Lowry theory acids/bases

In the Bronsted—Lowry acid—base theory, there is competition for an H+. Consider the acid—base reaction between acetic acid, a weak acid, and ammonia, a weak base ... 

Under the Bronsted-Lowry acid-base theory, acids are proton (H+) donors and bases are proton acceptors. 

O Jamie L. Adcock, "Teaching Bronsted-Lowry Acid-Base Theory in a Direct Comprehensive Way," /. Chem. Educ., Vol. 78,2001, 1495-1496. 

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 an aqueous solution, solvated hydrogen ions (hydro-nium ions, H3O ) react with hydroxide ions (OH") formed from the alkali to make two molecules of water. A salt is also formed. In non-aqueous reactions, water is not always formed however, there is always a donation of protons (see Bronsted-Lowry acid-base theory). 

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... 

Although Lewis and Bronsted bases comprise the same species, the same is not true of their acids. Lewis acids include bare metal cations, while Bronsted-Lowry acids do not. Also, Bell (1973) and Day Selbin (1969) have pointed out that Bronsted or protonic acids fit awkwardly into the Lewis definition. Protonic acids cannot accept an electron pair as is required in the Lewis definition, and a typical Lewis protonic add appears to be an adduct between a base and the add (Luder, 1940 Kolthoff, 1944). Thus, a protonic acid can only be regarded as a Lewis add in the sense that its reaction with a base involves the transient formation of an unstable hydrogen bond adduct. For this reason, advocates of the Lewis theory have sometimes termed protonic adds secondary acids (Bell, 1973). This is an unfortunate term for the traditional adds. 

From this discussion it can be seen that there is no ideal acid-base theory for AB cements and a pragmatic approach has to be adopted. Since the matrix is a salt, an AB cement can be defined quite simply as the product of the reaction of a powder and liquid component to yield a salt-like gel. The Bronsted-Lowry theory suffices to define all the bases and the protonic acids, and the Lewis theory to define the aprotic acids. The subject of acid-base balance in aluminosilicate glasses is covered by the Lux-Flood theory. 

C) The Bronsted-Lowry or proton theory interprets the acid-base reaction as a mere proton exchange between the acid (proton donor) and the base (proton acceptor) however, the Lewis theory or electron theory interprets the reaction as a donation and acceptance of a lone pair of electrons, where the... 

Acid-base behavior according to the Lewis theory has many of the same aspects as does acid-base theory according to the Bronsted-Lowry theory. 

According to the Arrhenius theory, acids (HA) are substances that dissociate in water to produce H + (aq). Bases (MOH) are substances that dissociate to yield OH aq). The more general Bransted-Lowry theory defines an acid as a proton donor, a base as a proton acceptor, and an acid-base reaction as a proton-transfer reaction. Examples of Bronsted-Lowry acids are HC1, NH4+, and HSO4- examples of Bronsted-Lowry bases are OH-, F-, and NH3. 

Today, when chemists use the words acid or base they refer to a model developed independently by Bronsted, Lowry, and Bjerrum. Since the most explicit statement of this theory was contained in the writings of Br /nsted, it is most commonly known as the Bronsted acid-base theory. 

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.,... 

Feb. 22,1879, Varde, Denmark - Dec. 17,1947, Copenhagen, Denmark) Ph.D. Copenhagen 1908, since 1908 Professor of Chemistry (the 3rd chair, i.e., the chair of Physical Chemistry at the Univ. of Copenhagen). 1926/27 visiting Professor at Yale Univ., New Haven, Connecticut, USA. Famous for his work on chemical reaction kinetics, chemical affinity, indicators, and thermodynamics of solutions. He could explain the effect of activity coefficients on reaction rates in solutions. In 1923 he developed independently of - Lowry, and - Bjerrum a new -> acid-base theory, the so-called Bronsted acid-base theory. 

Acid-base equilibrium — Using the Bronsted-Lowry definition (see -> acid-base theories), an acid-base reaction involves a -> proton transfer from an acid to a base. Removal of a proton from an acid forms its conjugate base, while addition of a proton to a base forms its conjugate acid. Acid-base equilibrium is achieved when the -> activity (or -> concentration) of each conjugate... 

Explain the differences between the Bronsted-Lowry and the Lewis acid-base theories, using the formation of the ammonium ion from ammonia and water to illustrate your points. 

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. 

Skill 10.1 Analyzing acids and bases according to acid-base theories (i.e., Arrhenius, Bronsted-Lowry, Lewis)... 

The Bronsted-Lowry theory provides a broader view of acid-base theory than does the Arrhenius theory. Bronsted-Lowry emphasizes the role of the solvent in the dissociation process. 9.29 a. HNOjfaij) + HjOf/) H3O+ (aq) + NOj-fflf )... 

A major problem with Arrhenius s acid-base theory is that some substances, like ammonia, produce basic solutions and react with acids, but do not contain hydroxide ions. In 1923 Johannes Bronsted, a Danish chemist, and Thomas Lowry, an English chemist, independently proposed a new way to define acids and bases. An acid donates hydrogen ions (also called a proton donor) a base accepts hydrogen ions (also called a proton acceptor). These definitions not only explain all the acids and bases covered by Arrhenius s theory, they also explain the basicity of ammonia and ions such as carbonate, and phosphate, P04 ... 

Perhaps you will not be surprised, then, you to learn that an even more general model of acids and bases was proposed by American chemist G. N. Lewis (1875-1946). Recall that Lewis developed the electron-pair theory of chemical bonding and introduced Lewis structures to keep track of the electrons in atoms and molecules. He applied his electron-pair theory of chemical bonding to acid-base reactions. Lewis proposed that an acid is an ion or molecule with a vacant atomic orbital that can accept (share) an electron pair. A base is an ion or molecule with a lone electron pair that it can donate (share). According to the Lewis model, a Lewis acid is an electron-pair acceptor and a Lewis base is an electron-pair donor. Note that the Lewis model includes all the substances classified as Bronsted-Lowry acids and bases and many more. 

In 1923 Bronsted and Lowry each developed an acid-base theory based on the central role of the proton. They defined an acid as a proton donor and a base as a proton acceptor. Thus, an acid-base reaction is one in which proton transfer occurs, i.e.. 

This classification was still not qrrite satisfadory for American chemist Gilbert Lewis (1875-1946)—or at least one corrld irrragine this had he not published his thoughts in the same year as Bronsted arrd Lowry (1923). Lewis notion was that hydrogen is present in many substances, but not all of them, whereas electrons are present in every substance. So, in the Lewis acid-base theory, electrons (or electron pairs, to be more precise) play central roles. In this theory a molectrle that can accept an electron pair plays the role of an acid. Conversely, a base can donate an electron pair ... 

As G. N. Lewis said, We frequently define an acid or a base as a substance whose aqueous solution gives, respectively, a higher concentration of hydrogen ion or hydroxide ion than that furnished by pure water. This is a very one-sided definition. In 1923, Bronsted and Lowry expanded the definitions of acids and bases to include species that do not involve solvent participation. According to the Bronsted-Lowry definition, an acid is any proton donor, whereas a base is any proton acceptor. This broader definition expanded acid-base theory to include gaseous species, such as HCI (g) and NH3 (g). It also allowed for the inclusion of acid-base reactions occurring in nonionizing solvents, such as benzene, as shown by Equation (14.6) ... 

The Lewis theory, by virtue of its broader definition of acids, allows acid—base theory to include all of the Bronsted-Lowry reactions and, as we shall see, a great many others. Most of the reactions we shall study in organic chemistry involve Lewis acid—base interactions, and a sound understanding of Lewis acid—base chemistry will help greatly. 

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. 

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