Brpnsted-Lowry acid

Carbonic acid, H2C03(aq), never exists as a pure compound it only exists as a species in aqueous solution, where it dissociates in just the same way as ethanoic acid in Equation (6.1) to form a solvated proton and the HCOj(aq) ion. Note how we form a solvated proton H30+(aq) by splitting a molecule of water, rather than merely donating a proton. Carbonic acid is, nevertheless, a Lowry-Brpnsted acid. 

Apart from the binary hydrides of Groups 16 and 17, Lowry/ Brpnsted acids in aqueous solution are nearly all oxoacids, i.e. substances containing O-H bonds which ionise in aqueous solution to give oxo-anions and H+(aq) (or H30+). Most oxoacids are molecular hydroxides E(OH) , such as B(OH)3, Ge(OH)4 and Te(OH)6, or oxohydroxides EOm(OH) . In addition, we have more complex species containing E-E bonds or E-O-E bridges. In EOm(OH) - for example, N02(0H), PO(OH)3, S02(0H)2,103(0H) - the m O atoms are held to E by bonds having at least some double bond character, via p -p or d -p overlap. Oxohydroxides may be seen as being derived from hydroxides by elimination of H20, and are favoured by elements E whose atoms form double bonds to O atoms. 

The same G N Lewis who gave us electron dot formulas also suggested a way of think mg about acids and bases that is more general than the Brpnsted-Lowry approach Where Brpnsted and Lowry viewed acids and bases as donors and acceptors of protons (positively charged) Lewis took the opposite view and focused on electron pairs (negatively charged) According to Lewis an acid is an electron pair acceptor and a base is an electron pair donor... 

An acid is defined as a proton donor within the Lowry-Brpnsted theory (see Chapter 6). Molecules of acid ionize in aqueous solution to form an anion and a proton, both of which are solvated. An acid such as ethanoic acid (VI) is said to be weak if the extent to which it dissociates is incomplete we call it strong if ionization is complete (see Section 6.2). 

Natural coal and oil contain many compounds of nitrogen. One of the worst products of their combustion is the acidic oxide of nitrogen, NO. At once, we are startled by this terminology, because the Lowry-Brpnsted definition of an acid involves the release of a proton, yet nitrogen monoxide NO has no proton to give. 

All aqueous solutions naturally contain hydroxide ions in consequence of the auto-protolytic reaction in Equation (6.2). As we have seen, there will be equal numbers of solvated protons and solvated hydroxide ions unless we add an acid or base to it. A solution containing more solvated protons than hydroxide ions is said to be an acid within the Lowry-Brpnsted theory, and a solution comprising more hydroxide ions than solvated protons is said to be a base. 

Brpnsted and Lowry classified acids as proton donors and bases as proton acceptors. HC1 is an acid (a proton donor) and it increases the concentration of H30+ in water ... 

In 1923, Brpnsted and Lowry defined acids and bases on the basis of the transfer of protons. A Brpnsted-Lowry acid is any species that can donate a proton, and a Brpnsted-Lowry base is any species that can accept a proton. These definitions also include all the Arrhenius acids and bases because compounds that dissociate to give H30+ are proton donors, and compounds that dissociate to give OH are proton acceptors. (Hydroxide ion accepts a proton to form H20.)... 

Brpnsted-Lowry Definition Acids are proton (H1+) donors. Bases are proton (H1+) acceptors. 

In 1923, Johannes N. Brpnsted (1879-1947) and Thomas M. Lowry (1874-1936) independently defined acids and bases in a different way from the Arrhenins definitions. The resulting theory is sometimes called the Brpnsted-Lowry theory, bnt more often is referred to as just the Brpnsted theory. The Brpnsted theory extends the definitions of acid and base in a way that explains more than the Arrhenins definitions can explain. According to this theory, a Brpnsted acid is a proton donor, and a Brpnsted base is a proton acceptor. 

A mechanism for this reaction has been proposed and is summarized in Sch. 10. The catalyst 64 is thought to be bifunctional with the aluminum center operating as a Lewis acid and the lithium naphthoxide operating as a Lowry-Brpnsted base. It was envisaged that the aldehyde coordinates with the aluminum to give the complex 69 and deprotonation of the dimethyl phosphite then gives the aggregate 70 in which the phosphite anion is positioned for P-alkylation of the aldehyde that will occur selectively from the si face when the catalyst is prepared from (f )-BINOL. 

See pH. When dealing with chemical reactions in solvents other than water, it is sometimes convenient to define an acid as a substance that ionizes to give the positive ion of the solvent. The common definitions of acid have been extended as more detailed studies of chemical reactions have been made. The Lowry-Brpnsted definition of an acid as a substance that can give up a proton is more useful in connection with an understanding of bases (see base). Perhaps the most significant contribution to the theory of acids was the electron-pair concept introduced by G. N. Lewis around 1915. 

From a kinetic standpoint, acid-base reactions are among the fastest reactions known, especially in aqueous solvents. They are also used to generate reactive intermediates that can be part of other reaction types. Acids are attacked by Lewis or Brpnsted-Lowry bases. Acid-base reactions are integral to many reactions, but they are not always easy to describe by a specific transform since they may be an adjunct to the desired... 

According to Brpnsted and Lowry, an acid-base reaction is defined in terms of a proton transfer. By this definition, the reaction of HCl in water is the following ... 

In the aqueous system, the Brpnsted-Lowry definitions of acids and bases are of general applicability. A Brpnsted acid a proton donor. Acidic oxides react with water to produce oxonium ions in solution, e.g. 

In this reaction in aqueous solution, a proton, H, is transferred from the H30 ion to the NH3 molecule, giving H2O and NH4 (Figure 16.3). Here H30 is the proton donor, or acid, and NH3 is the proton acceptor, or base. Note that in the Brpnsted— Lowry concept, acids (and bases) can be ions as well as molecular substances. 

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. 

According to Brpnsted and Lowry, an acid is a species that loses a proton, and a base is a species that gains a proton. (Remember that positively charged hydrogen ions are called protons.) For example, in the reaction shown next, hydrogen chloride (HCl) is an acid because it loses a proton, and water is a base because it gains a proton. In the... 

According to the Brpnsted-Lowry theory, acids are H donors and bases are H acceptors. 

The following definition was given independently in 1923 by the two chemists Brpnsted and Lowry. An acid is a proton donor according to the equation... 

Unlike the situation for Brpnsted acidity, manifest by complete or partial proton transfer from acid to base, Lewis acidity is a more general concept. It encompasses the Brpnsted-Lowry definition and thus there is no universal scale (in contrast to the Hammett acidity... 

A more general theory of acids and bases was devised independently by Johannes Br0n sted (Denmark) and Thomas M Lowry (England) m 1923 In the Brpnsted-Lowry approach an acid is a proton donor, and a base is a proton acceptor The reaction that occurs between an acid and a base is proton transfer... 

The acid dissociation constant has the same form m Brpnsted-Lowry as m the Arrhenius approach but is expressed m the concentration of H30" rather than The concentration terms [H30" ] and [H" ] are considered equivalent quantities m equilibrium constant expressions... 

Analyzing acid-base reactions according to the Brpnsted-Lowry picture provides yet another benefit Table 1 7 which lists acids according to their strength m descending... 

This chapter sets the stage for all of the others by reminding us that the relationship between structure and properties is what chemistry is all about It begins with a review of Lewis structures moves to a discussion of the Arrhenius Brpnsted-Lowry and Lewis pictures of acids and bases and the effects of structure on acidity and basicity... 

Section 1 13 According to the Brpnsted-Lowry definitions an acid is a proton donor and a base is a proton acceptor... 

Basicity constants are not necessary in the Brpnsted-Lowry approach Basicity is measured according to the pA of the conjugate acid The weaker the conjugate acid the stronger the base... 

This IS a very useful relationship You should practice writing equations according to the Brpnsted-Lowry definitions of acids and bases and familiarize yourself with Table 1 7 which gives the s of various Br0n sted acids... 

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. 

A Br0nsted-Lowry base is to a hydrogen-ion acceptor as a Brpnsted-Lowry acid is to —... 

When water acts as a Brpnsted-Lowry acid, it donates a proton to another species, thereby converting to the hydroxide ion. 

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