Arrhenius concept of acids and bases

The species is shown here hydrogen-bonded to three water molecules.The positive charge shown is actually distributed over the ion. 

We introduced strong and weak acids and bases in Section 4A. 

The special role of the hydronium ion (or hydrogen ion) and the hydroxide ion in aqueous solutions arises from the following reaction  

The addition of acids and bases alters the concentrations of these ions in water. 

In Arrhenius s theory, a strong acid is a substance that completely ionizes in aqueous solution to give H30 (a ) and an anion. An example is perchloric acid, HCIO4. 

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There are certain limitations of the Arrhenius concept of acids and bases. Acids and bases have been described in terms of their aqueous solutions and not in terms of the entities themselves. The theory is thus applicable exclusively to aqueous solutions. An entity such as HC1 is accounted as an acid only when it is dissolved in water if dissolved in... 

The first person to recognize the essential nature of acids and bases was Svante Arrhenius. Based on his experiments with electrolytes, Arrhenius postulated that acids produce hydrogen ions in aqueous solution, and bases produce hydroxide ions. At the time of its discovery the Arrhenius concept of acids and bases was a major step forward in quantifying acid—base chemistry, but this concept is limited because it applies only to aqueous solutions and allows for only one kind of base—the hydroxide ion. A more general definition of acids and bases was suggested independently by the Danish chemist Johannes N. Bronsted (1879-1947) and the English chemist Thomas M. Lowry (1874-1936) in 1923. In terms of the Bronsted—Lowry definition, an acid is a proton (H+) donor, and a base is a proton acceptor. For example, when gaseous HCl dissolves in water, each HCl molecule donates a proton to a water molecule, and so HCl qualifies as a Bronsted-Lowry acid. The molecule that accepts the proton—water in this case—is a Bronsted-Lowry base. 

If you missed 43, go to The Arrhenius Concept of Acids and Bases, page 394. 

The Arrhenius concept of acids and bases was a tremendous advance in the understanding of these compounds, but is it limited to aqueous solutions, and a lot of chemistry takes place out of water. In 1923 a Danish chemist, Johannes Bronsted (1879-1947), and an English chemist, Thomas Lowry (1874-1936), proposed a more general way to describe acids and bases centered on the ability of a species to donate or accept a proton, IT. It was not limited to aqueous solutions. Here is how they defined acids, bases and neutralization ... 

In the Arrhenius concept of acids and bases, what species are produced by acids and bases in water What is formed from these species in neutralization ... 

Although the Arrhenius concept of acids and bases was a major step forward in understanding acid-base chemistry, this concept is limited because it allows for only one kind of base—the hydroxide ion. A more general definition of acids and bases was suggested by the Danish chemist Johannes Bronsted and the English chemist Thomas Lowry. 

Arrhenius concept of acids and bases a concept postulating that acids produce hydrogen ions in solution, whereas bases produce hydroxide ions in solution. 

Arrhenius concept of acids and bases (16.1) Bronsted-Lowry model (16.1) conjugate acid (16.1) conjugate base (16.1) conjugate acid-base pair (16.1)... 

By 1830 it was evident that all acids contain hydrogen but not all hydrogen-containing substances are acids. During the 1880s, the Swedish chemist Svante Arrhenius (1859-1927) defined acids as substances that produce lU ions in water and bases as substances that produce OH ions in water. Over time the Arrhenius concept of acids and bases came to be stated in the following way ... 

Apart from this modification, the Arrhenius definitions of acid and base are still valid and useful today, as long as we are talking about aqueous solutions. However, the Arrhenius concept of acids and bases is so intimately tied to reactions that take place in water that it has no good way to deal with acid-base reactions in nonaqueous solutions. For this reason, we concentrate in this chapter on the Bronsted-Lowry definitions of acids and bases, which are more useful to us in our discussion of reactions of organic compounds. 

Although the Arrhenius concept of acids and bases is useful, it is somewhat limited. For example, it tends to single out the OH ion as the source of base character, when other ions or molecules can play a similar role. In 1923, Johannes N. Brpnsted and Thomas M. Lowry independently noted that many reactions involve nothing more than the transfer of a proton (H ) between reactants, and they reaUzed that they could use this idea to expand the definitions of acids and bases to describe a large class of chemical reactions. In this view, acid—base reactions are proton-transfer reactions. 

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